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Papers by Wafaa Fawzy

Journal of Chemical Physics, Apr 18, 2007

The NH–N2 van der Waals complex has been examined at the CCSD(T) level of theory using aug-cc-pVD... more The NH–N2 van der Waals complex has been examined at the CCSD(T) level of theory using aug-cc-pVDZ and aug-cc-pVTZ basis sets. The full basis set superposition error correction was applied. Two minimum energy structures were located for the electronic ground state. The global minimum corresponds to a linear geometry of the complex (NH–N–N), with De=236cm−1 and Rc.m.=4.22Å. The secondary minimum corresponds to a T-shaped geometry of C2v symmetry, where the nitrogen atom of the H–N moiety points toward the center of mass of the N2 unit, aligned with the a-inertial axis of the complex. The binding energy and Rc.m. value for the secondary minimum were 144cm−1 and 3.63Å, respectively. This potential energy surface is consistent with the properties of matrix-isolated NH–N2, and it is predicted that linear NH–N2 will be a stable complex in the gas phase at low temperatures.

Journal of Chemical Physics, Apr 24, 2006

In this paper, we present the first correlated ab initio investigations on the ground electronic ... more In this paper, we present the first correlated ab initio investigations on the ground electronic state of the O2–HF complex. Calculations were performed using the CCSD(T) method with the aug-cc-pVDZ and aug-cc-pVTZ basis sets. The results show that there are two equivalent minimum energy hydrogen-bonded structures of planar bent geometry, where the minima correspond to exchange of the oxygen atoms. For each minimum the length of the O–H hydrogen bond is 2.16Å. The best calculated value of De of the equivalent minima is 271cm−1. The T-shaped geometry of the complex, with oxygen perpendicular to the axis connecting the center of masses of O2 and the HF molecule, represents a barrier to tunneling between the equivalent minima. The best estimated value of that barrier height is 217cm−1. The linear O–O–HF geometry of the complex represents a saddle point. The calculated geometrical parameters of the minimum energy structure of the complex are in reasonable agreement with the previously reported spectroscopic results. However, results of the current calculations suggest that a full understanding of the fine structures of the observed infrared spectrum of the complex requires the development of an effective Hamiltonian that takes the effects of tunneling into account.

Journal of Molecular Spectroscopy, Sep 1, 1989

This paper concerns rotational energy levels and line intensities for electronic, vibrational, an... more This paper concerns rotational energy levels and line intensities for electronic, vibrational, and microwave transitions in an open-shell complex consisting of an open-shell diatomic molecule and a closed-shell partner. The electronic state of the open-shell diatomic fragment is a 2Sϩ1 ⌺ state, where S Ն 1 2 , the close-shell partner could be a rare gas atom or a diatomic molecule or a planar polyatomic molecule. We are considering a near-rigid rotor model for a nonlinear complex, taking into account thoroughly all effects of the electron spin and the quartic centrifugal distortion correction terms. The total Hamiltonian is expressed as HϭH rot ϩH sr ϩH ss ϩH cd ϩH srcd ϩH sscd. We have derived all the nonvanishing matrix elements of the Hamiltonian operators in the molecular basis set. The rotational energy levels are calculated by numerical diagonalization of the total Hamiltonian matrix for each J value. The nonvanishing matrix elements of the electric dipole moment operator are derived in the molecular basis set for electronic, vibrational, and microwave transitions within the complex. Expectation values of the quantum numbers and of the parities of the rotational states are derived in the molecular basis set. Relative intensities of the allowed rotational transitions, expectation values of the quantum numbers and the parities are calculated numerically in the space of the eigenvectors obtained from diagonalization of the Hamiltonian matrix. The formalism and the computer program of this paper are considered as extensions to our previous work [

Journal of Chemical Physics, Jan 3, 2013

This work reports the first highly correlated ab initio study of the intermolecular and intramole... more This work reports the first highly correlated ab initio study of the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the rmO2−(rmX2Pirmg)−rmHF(rmX1Sigma+){\rm O}_2^ - ({\rm X}{}^2\Pi _{\rm g}) - {\rm HF}({\rm X}{}^1\Sigma^+)rmO2−(rmX2Pirmg)−rmHF(rmX1Sigma+)O2−(XΠg2)− HF (XΣ+1) complex. Accurate electronic structure calculations were performed using the coupled cluster method including single and double excitations with addition of the perturbative triples correction [CCSD(T)] with the Dunning's correlation consistent basis sets aug-cc-pVnZ, n = 2–5. Also, the explicitly correlated CCSD(T)-F12a level of theory was employed with the AVnZ basis as well as the Peterson and co-workers VnZ-F12 basis sets with n = 2 and 3. Results of all levels of calculations predicted two equivalent minimum energy structures of planar geometry and Cs symmetry along the A″ surface of the complex, whereas the A′ surface is repulsive. Values of the geometrical parameters and the counterpoise corrected dissociation energies (Cp-De) that were calculated using the CCSD(T)-F12a/VnZ-F12 level of theory are in excellent agreement with those obtained from the CCSD(T)/aug-cc-pV5Z calculations. The minimum energy structure is characterized by a very short hydrogen bond of length of 1.328 Å, with elongation of the HF bond distance in the complex by 0.133 Å, and De value of 32.313 Kcal/mol. Mulliken atomic charges showed that 65% of the negative charge is localized on the hydrogen bonded end of the superoxide radical and the HF unit becomes considerably polarized in the complex. These results suggest that the hydrogen bond is an incipient ionic bond. Exploration of the potential energy surface confirmed the identified minimum and provided support for vibrationally induced intramolecular proton transfer within the complex. The T-shaped geometry that possesses C2v symmetry presents a saddle point on the top of the barrier to the in-plane bending of the hydrogen above and below the axis that connects centers of masses of the monomers. The height of this barrier is 7.257 Kcal/mol, which is higher in energy than the hydrogen bending frequency by 909.2 cm−1. The calculated harmonic oscillator vibrational frequencies showed that the H–F stretch vibrational transition in the complex is redshifted by 2564 cm−1 and gained significant intensity (by at least a factor of 30) with respect to the transition in the HF monomer. These results make the rmO2−−rmHF{\rm O}_2^ - - {\rm HF}rmO2−−rmHFO2−− HF complex an excellent prototype for infrared spectroscopic investigations on open-shell complexes with vibrationally induced proton transfer.

Journal of Chemical Physics, Sep 1, 1990

The HF stretching band of the NO–HF open-shell complex has been recorded using a molecular-beam o... more The HF stretching band of the NO–HF open-shell complex has been recorded using a molecular-beam optothermal spectrometer. The spectrum exhibits P-type doubling indicative of an unpaired electron spin coupled to the rotational angular momentum of a bent complex with substantially quenched electron orbital angular momentum. From B̄″=0.111 320(17) cm−1, and an off-axis angle for the NO of 30°, the zero-point center-of-mass separation is estimated to be 3.4396(3) Å. The HF frequency shift of 84 cm−1 indicates that the complex is hydrogen bonded, and the spectral intensities imply that the HF axis is aligned closely to the center-of-mass axis and the NO is off axis by 30±15°. The Renner–Teller-like orbital quenching parameter is somewhat larger than the spin–orbit constant in the free NO molecule and increases substantially upon vibrational excitation. The transitions in this band exhibit vibrational predissociation broadening of 200±40 MHz (FWHM), similar to that observed for a number of closed-shell hydrogen-bonded HF complexes.

Journal of Chemical Physics, Jun 15, 1990

The infrared absorption spectrum of the ν3 fundamental band of the CD3 radical has been detected ... more The infrared absorption spectrum of the ν3 fundamental band of the CD3 radical has been detected by diode laser absorption spectroscopy. The CD3 radical was produced by excimer laser photolysis of CD3I at 248 nm or (CD3)2CO at 193 nm. Molecular parameters of the v3=1 vibrational state were determined from a least-squares fit to 62 rotation–vibration transitions. In this fit, molecular parameters describing the ground state were constrained to those obtained from previous spectroscopic studies of the ν2 parallel IR band [J. M. Frye, T. J. Sears, and D. Leitner, J. Chem. Phys. 88, 5300 (1988)]. The molecular parameters determined in the present work are the band origin ν0=2381.088 60(84), B′=4.758 737(40), C′=2.373 297(34), (ζC)3=0.476 278(72), q3=0.003 76(59), D′N =0.000 187 9(5), DNK =−0.000 341 0(12), D′K =0.000 143 7(8), ηN =−0.000 005 5(36), η′K =0.000 060(35), and qN =0.000 063(17), all in cm−1 with one standard deviation in parentheses. The derived molecular parameters were compared with those for the CH3 radical v3=1 level determined previously [T. Amano, P. Bernath, C. Yamada, Y. Endo, and E. Hirota, J. Chem. Phys. 77, 5284 (1982)]. The molecular parameters of the v3=1 state of the CD3 and CH3 radicals follow the expected isotopic relationships. We have also found that the determined molecular parameters reasonably satisfy the approximate planarity relationships [J. K. G. Watson, J. Mol. Spectrsoc. 65, 123 (1977)] and the sign of the l-type doubling constant is consistent with a planar equilibrium structure.

The group IIA metals have stable hypermetallic oxides of the general form MOM. Theoretical intere... more The group IIA metals have stable hypermetallic oxides of the general form MOM. Theoretical interest in these species is associated with the multi-reference character of the ground states. It is now established that the ground states can be formally assigned to the M + O 2− M + configuration, which leaves two electrons in orbitals that are primarily metal-centered ns orbitals. Hence the MOM species are diradicals with very small energy spacings between the lowest energy singlet and triplet states. Previously, we have characterized the lowest energy singlet transition (1 Σ + u ← X 1 Σ + g) of BeOBe. In this study we obtained the first electronic spectrum of CaOCa. Jet-cooled laser induced fluorescence spectra were recorded for multiple bands that occured within the 14,800-15,900 cm −1 region. Most of the bands exhibited simple P/R branch rotational line patterns that were blue-shaded. Only even rotational levels were observed, consistent with the expected X 1 Σ + g symmetry of the ground state (40 Ca has zero nuclear spin). A progression of excited bending modes was evident in the spectrum, indicating that the transition is to an upper state that has a bent equilibrium geometry. Molecular constants were extracted from the rovibronic bands using PGOPHER. The experimental results and interpretation of the spectrum, which was guided by the predictions of electronic structure calculation, will be presented.

1^{1}1 This research was supported by the U.S. National Science Foundation. Address of Fawzy and ... more $^{1}$ This research was supported by the U.S. National Science Foundation. Address of Fawzy and schwendeman: Department of Chemistry, Michigan State University, East Lansing, MI 48824.

1^{1}1W. Fawzy, R. J. Le Roy, B Simard, H. Niki and P. A. Hackett, J. Chem. Phys. (submitted 1992... more $^{1}$W. Fawzy, R. J. Le Roy, B Simard, H. Niki and P. A. Hackett, J. Chem. Phys. (submitted 1992). 2^{2}2M. S. Child, H. Ess\'{e}n and R. J. Le Roy, J. Chem. Phys. 78,6732(1983). 3^{3}3R. J. Le Roy, R. G. Macdonald and G. Burns, J. Chem. Phys. 65, 1485 (1976). 4^{4}4R. J. Le Roy, Comp. Phys. Comm. 52, 383 (1989).

ast^{\ast}astThis research was supported by the U.S. National Science Foundation.Author Institution: ... more $^{\ast}$This research was supported by the U.S. National Science Foundation.Author Institution: Department of Chemistry, Michigan State UniversityApproximately 120 pure quadrupole transitions in more than 6 vibrational states in CF,1 have been observed by means of an infrared-radio-frequency double resonance spectrometer operating near 1075cm−11075 cm^{-1}1075cm−1. Double-resonance spectra were observed for five 12C14O2^{12}C^{14}O_{2}12C14O2 and three 12C15O2^{12}C^{15}O_{2}12C15O2 laser lines. The radio frequency source was a 1-500 MHz computer-controlled frequency synthesizer. Although preliminary spectra were recorded with an intra-cavity coaxial cell, the best spectra were obtained with an extra-cavity cell of stripline design. The quadrupole hyperfine structure was calculated by direct diagonalization of the energy matrices. Quadrupole coupling constants obtained for the ground and several excited vibrational states will be compared with previous results obtained by other spectroscopic techniques

Computational and Theoretical Chemistry, 2021

1^{1}1 This research was supported by the U.S. National Science Foundation. Address of Fawzy and ... more $^{1}$ This research was supported by the U.S. National Science Foundation. Address of Fawzy and Schwendeman: Department of Chemistry, Michigan State University, East Lansing, MI 48824.

Author Institution: Department of Chemistry, East Tennessee State University, Johnson City, TN 37... more Author Institution: Department of Chemistry, East Tennessee State University, Johnson City, TN 37504; Department of Chemistry, Emory University, Atlanta, GA 30322

Author Institution: Optical Technology Division, National Institute of Standards and Technology; ... more Author Institution: Optical Technology Division, National Institute of Standards and Technology; Faculty of Science, University of United Arab Emirates

Author Institution: Optical Technology Division, National Institute of Standards and Technology; ... more Author Institution: Optical Technology Division, National Institute of Standards and Technology; University of United Arab Emirates, Faculty of Science; Department of Chemistry, Wesleyan University

Proceedings of the 71st International Symposium on Molecular Spectroscopy, 2016

The Journal of Chemical Physics, 2013

This work reports the first highly correlated ab initio study of the intermolecular and intramole... more This work reports the first highly correlated ab initio study of the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O(2)(-)(X(2)Π(g))-HF(X(1)Σ(+)) complex. Accurate electronic structure calculations were performed using the coupled cluster method including single and double excitations with addition of the perturbative triples correction [CCSD(T)] with the Dunning's correlation consistent basis sets aug-cc-pVnZ, n = 2-5. Also, the explicitly correlated CCSD(T)-F12a level of theory was employed with the AVnZ basis as well as the Peterson and co-workers VnZ-F12 basis sets with n = 2 and 3. Results of all levels of calculations predicted two equivalent minimum energy structures of planar geometry and C(s) symmetry along the A" surface of the complex, whereas the A' surface is repulsive. Values of the geometrical parameters and the counterpoise corrected dissociation energies (Cp-D(e)) that were calculated using the CCSD(T)-F12a/VnZ-F12 level of theory are in excellent agreement with those obtained from the CCSD(T)/aug-cc-pV5Z calculations. The minimum energy structure is characterized by a very short hydrogen bond of length of 1.328 Å, with elongation of the HF bond distance in the complex by 0.133 Å, and D(e) value of 32.313 Kcal/mol. Mulliken atomic charges showed that 65% of the negative charge is localized on the hydrogen bonded end of the superoxide radical and the HF unit becomes considerably polarized in the complex. These results suggest that the hydrogen bond is an incipient ionic bond. Exploration of the potential energy surface confirmed the identified minimum and provided support for vibrationally induced intramolecular proton transfer within the complex. The T-shaped geometry that possesses C(2v) symmetry presents a saddle point on the top of the barrier to the in-plane bending of the hydrogen above and below the axis that connects centers of masses of the monomers. The height of this barrier is 7.257 Kcal/mol, which is higher in energy than the hydrogen bending frequency by 909.2 cm(-1). The calculated harmonic oscillator vibrational frequencies showed that the H-F stretch vibrational transition in the complex is redshifted by 2564 cm(-1) and gained significant intensity (by at least a factor of 30) with respect to the transition in the HF monomer. These results make the O(2)(-)-HF complex an excellent prototype for infrared spectroscopic investigations on open-shell complexes with vibrationally induced proton transfer.

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The Journal of Chemical Physics, 2009

This work presents the first high level correlated ab initio study of the intermolecular potentia... more This work presents the first high level correlated ab initio study of the intermolecular potential energy surface of the ground electronic state of the O(2) (X (3)Sigma(g)(-))-H(2)(X) complex. This computational study was carried out using the CCSD(T) level of theory with the aug-cc-pVXZ basis sets, where X = D, T, Q, and 5. All calculated energies were corrected using the BSSE method. The lowest energy geometry and the shape of the intermolecular potential energy surface showed significant dependence on the size of the basis set as well as the BSSE corrections. The most accurate results were obtained using the CCSD(T)/aug-cc-pVQZ and CCSD(T)/aug-cc-pV5Z combinations with the BSSE corrections. These calculations yield a global minimum of C(2v) symmetry, where internuclear axes of the O(2) and H(2) moieties are parallel to each other. For this geometry, the D(e) value is 65.27(30) cm(-1), which is in excellent agreement with the CBS limit of 65.14 cm(-1). The distance between centers of masses of the H(2) and O(2) monomers within the complex is 3.225(1) A. Barrier heights to rotation of the H(2) and O(2) units by 180 degrees about the axis that connects their centers of masses are 24 and 159 cm(-1), respectively. The current results should stimulate microwave spectroscopic detection of the O(2)-H(2) complex.

The Journal of Chemical Physics, 2005

The H¢-NH(£) van der Waals complex has been examined using ab initio theory and detected via fluo... more The H¢-NH(£) van der Waals complex has been examined using ab initio theory and detected via fluorescence excitation spectroscopy of the

Journal of Chemical Physics, Apr 18, 2007

The NH–N2 van der Waals complex has been examined at the CCSD(T) level of theory using aug-cc-pVD... more The NH–N2 van der Waals complex has been examined at the CCSD(T) level of theory using aug-cc-pVDZ and aug-cc-pVTZ basis sets. The full basis set superposition error correction was applied. Two minimum energy structures were located for the electronic ground state. The global minimum corresponds to a linear geometry of the complex (NH–N–N), with De=236cm−1 and Rc.m.=4.22Å. The secondary minimum corresponds to a T-shaped geometry of C2v symmetry, where the nitrogen atom of the H–N moiety points toward the center of mass of the N2 unit, aligned with the a-inertial axis of the complex. The binding energy and Rc.m. value for the secondary minimum were 144cm−1 and 3.63Å, respectively. This potential energy surface is consistent with the properties of matrix-isolated NH–N2, and it is predicted that linear NH–N2 will be a stable complex in the gas phase at low temperatures.

Journal of Chemical Physics, Apr 24, 2006

In this paper, we present the first correlated ab initio investigations on the ground electronic ... more In this paper, we present the first correlated ab initio investigations on the ground electronic state of the O2–HF complex. Calculations were performed using the CCSD(T) method with the aug-cc-pVDZ and aug-cc-pVTZ basis sets. The results show that there are two equivalent minimum energy hydrogen-bonded structures of planar bent geometry, where the minima correspond to exchange of the oxygen atoms. For each minimum the length of the O–H hydrogen bond is 2.16Å. The best calculated value of De of the equivalent minima is 271cm−1. The T-shaped geometry of the complex, with oxygen perpendicular to the axis connecting the center of masses of O2 and the HF molecule, represents a barrier to tunneling between the equivalent minima. The best estimated value of that barrier height is 217cm−1. The linear O–O–HF geometry of the complex represents a saddle point. The calculated geometrical parameters of the minimum energy structure of the complex are in reasonable agreement with the previously reported spectroscopic results. However, results of the current calculations suggest that a full understanding of the fine structures of the observed infrared spectrum of the complex requires the development of an effective Hamiltonian that takes the effects of tunneling into account.

Journal of Molecular Spectroscopy, Sep 1, 1989

This paper concerns rotational energy levels and line intensities for electronic, vibrational, an... more This paper concerns rotational energy levels and line intensities for electronic, vibrational, and microwave transitions in an open-shell complex consisting of an open-shell diatomic molecule and a closed-shell partner. The electronic state of the open-shell diatomic fragment is a 2Sϩ1 ⌺ state, where S Ն 1 2 , the close-shell partner could be a rare gas atom or a diatomic molecule or a planar polyatomic molecule. We are considering a near-rigid rotor model for a nonlinear complex, taking into account thoroughly all effects of the electron spin and the quartic centrifugal distortion correction terms. The total Hamiltonian is expressed as HϭH rot ϩH sr ϩH ss ϩH cd ϩH srcd ϩH sscd. We have derived all the nonvanishing matrix elements of the Hamiltonian operators in the molecular basis set. The rotational energy levels are calculated by numerical diagonalization of the total Hamiltonian matrix for each J value. The nonvanishing matrix elements of the electric dipole moment operator are derived in the molecular basis set for electronic, vibrational, and microwave transitions within the complex. Expectation values of the quantum numbers and of the parities of the rotational states are derived in the molecular basis set. Relative intensities of the allowed rotational transitions, expectation values of the quantum numbers and the parities are calculated numerically in the space of the eigenvectors obtained from diagonalization of the Hamiltonian matrix. The formalism and the computer program of this paper are considered as extensions to our previous work [

Journal of Chemical Physics, Jan 3, 2013

This work reports the first highly correlated ab initio study of the intermolecular and intramole... more This work reports the first highly correlated ab initio study of the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the rmO2−(rmX2Pirmg)−rmHF(rmX1Sigma+){\rm O}_2^ - ({\rm X}{}^2\Pi _{\rm g}) - {\rm HF}({\rm X}{}^1\Sigma^+)rmO2−(rmX2Pirmg)−rmHF(rmX1Sigma+)O2−(XΠg2)− HF (XΣ+1) complex. Accurate electronic structure calculations were performed using the coupled cluster method including single and double excitations with addition of the perturbative triples correction [CCSD(T)] with the Dunning's correlation consistent basis sets aug-cc-pVnZ, n = 2–5. Also, the explicitly correlated CCSD(T)-F12a level of theory was employed with the AVnZ basis as well as the Peterson and co-workers VnZ-F12 basis sets with n = 2 and 3. Results of all levels of calculations predicted two equivalent minimum energy structures of planar geometry and Cs symmetry along the A″ surface of the complex, whereas the A′ surface is repulsive. Values of the geometrical parameters and the counterpoise corrected dissociation energies (Cp-De) that were calculated using the CCSD(T)-F12a/VnZ-F12 level of theory are in excellent agreement with those obtained from the CCSD(T)/aug-cc-pV5Z calculations. The minimum energy structure is characterized by a very short hydrogen bond of length of 1.328 Å, with elongation of the HF bond distance in the complex by 0.133 Å, and De value of 32.313 Kcal/mol. Mulliken atomic charges showed that 65% of the negative charge is localized on the hydrogen bonded end of the superoxide radical and the HF unit becomes considerably polarized in the complex. These results suggest that the hydrogen bond is an incipient ionic bond. Exploration of the potential energy surface confirmed the identified minimum and provided support for vibrationally induced intramolecular proton transfer within the complex. The T-shaped geometry that possesses C2v symmetry presents a saddle point on the top of the barrier to the in-plane bending of the hydrogen above and below the axis that connects centers of masses of the monomers. The height of this barrier is 7.257 Kcal/mol, which is higher in energy than the hydrogen bending frequency by 909.2 cm−1. The calculated harmonic oscillator vibrational frequencies showed that the H–F stretch vibrational transition in the complex is redshifted by 2564 cm−1 and gained significant intensity (by at least a factor of 30) with respect to the transition in the HF monomer. These results make the rmO2−−rmHF{\rm O}_2^ - - {\rm HF}rmO2−−rmHFO2−− HF complex an excellent prototype for infrared spectroscopic investigations on open-shell complexes with vibrationally induced proton transfer.

Journal of Chemical Physics, Sep 1, 1990

The HF stretching band of the NO–HF open-shell complex has been recorded using a molecular-beam o... more The HF stretching band of the NO–HF open-shell complex has been recorded using a molecular-beam optothermal spectrometer. The spectrum exhibits P-type doubling indicative of an unpaired electron spin coupled to the rotational angular momentum of a bent complex with substantially quenched electron orbital angular momentum. From B̄″=0.111 320(17) cm−1, and an off-axis angle for the NO of 30°, the zero-point center-of-mass separation is estimated to be 3.4396(3) Å. The HF frequency shift of 84 cm−1 indicates that the complex is hydrogen bonded, and the spectral intensities imply that the HF axis is aligned closely to the center-of-mass axis and the NO is off axis by 30±15°. The Renner–Teller-like orbital quenching parameter is somewhat larger than the spin–orbit constant in the free NO molecule and increases substantially upon vibrational excitation. The transitions in this band exhibit vibrational predissociation broadening of 200±40 MHz (FWHM), similar to that observed for a number of closed-shell hydrogen-bonded HF complexes.

Journal of Chemical Physics, Jun 15, 1990

The infrared absorption spectrum of the ν3 fundamental band of the CD3 radical has been detected ... more The infrared absorption spectrum of the ν3 fundamental band of the CD3 radical has been detected by diode laser absorption spectroscopy. The CD3 radical was produced by excimer laser photolysis of CD3I at 248 nm or (CD3)2CO at 193 nm. Molecular parameters of the v3=1 vibrational state were determined from a least-squares fit to 62 rotation–vibration transitions. In this fit, molecular parameters describing the ground state were constrained to those obtained from previous spectroscopic studies of the ν2 parallel IR band [J. M. Frye, T. J. Sears, and D. Leitner, J. Chem. Phys. 88, 5300 (1988)]. The molecular parameters determined in the present work are the band origin ν0=2381.088 60(84), B′=4.758 737(40), C′=2.373 297(34), (ζC)3=0.476 278(72), q3=0.003 76(59), D′N =0.000 187 9(5), DNK =−0.000 341 0(12), D′K =0.000 143 7(8), ηN =−0.000 005 5(36), η′K =0.000 060(35), and qN =0.000 063(17), all in cm−1 with one standard deviation in parentheses. The derived molecular parameters were compared with those for the CH3 radical v3=1 level determined previously [T. Amano, P. Bernath, C. Yamada, Y. Endo, and E. Hirota, J. Chem. Phys. 77, 5284 (1982)]. The molecular parameters of the v3=1 state of the CD3 and CH3 radicals follow the expected isotopic relationships. We have also found that the determined molecular parameters reasonably satisfy the approximate planarity relationships [J. K. G. Watson, J. Mol. Spectrsoc. 65, 123 (1977)] and the sign of the l-type doubling constant is consistent with a planar equilibrium structure.

The group IIA metals have stable hypermetallic oxides of the general form MOM. Theoretical intere... more The group IIA metals have stable hypermetallic oxides of the general form MOM. Theoretical interest in these species is associated with the multi-reference character of the ground states. It is now established that the ground states can be formally assigned to the M + O 2− M + configuration, which leaves two electrons in orbitals that are primarily metal-centered ns orbitals. Hence the MOM species are diradicals with very small energy spacings between the lowest energy singlet and triplet states. Previously, we have characterized the lowest energy singlet transition (1 Σ + u ← X 1 Σ + g) of BeOBe. In this study we obtained the first electronic spectrum of CaOCa. Jet-cooled laser induced fluorescence spectra were recorded for multiple bands that occured within the 14,800-15,900 cm −1 region. Most of the bands exhibited simple P/R branch rotational line patterns that were blue-shaded. Only even rotational levels were observed, consistent with the expected X 1 Σ + g symmetry of the ground state (40 Ca has zero nuclear spin). A progression of excited bending modes was evident in the spectrum, indicating that the transition is to an upper state that has a bent equilibrium geometry. Molecular constants were extracted from the rovibronic bands using PGOPHER. The experimental results and interpretation of the spectrum, which was guided by the predictions of electronic structure calculation, will be presented.

1^{1}1 This research was supported by the U.S. National Science Foundation. Address of Fawzy and ... more $^{1}$ This research was supported by the U.S. National Science Foundation. Address of Fawzy and schwendeman: Department of Chemistry, Michigan State University, East Lansing, MI 48824.

1^{1}1W. Fawzy, R. J. Le Roy, B Simard, H. Niki and P. A. Hackett, J. Chem. Phys. (submitted 1992... more $^{1}$W. Fawzy, R. J. Le Roy, B Simard, H. Niki and P. A. Hackett, J. Chem. Phys. (submitted 1992). 2^{2}2M. S. Child, H. Ess\'{e}n and R. J. Le Roy, J. Chem. Phys. 78,6732(1983). 3^{3}3R. J. Le Roy, R. G. Macdonald and G. Burns, J. Chem. Phys. 65, 1485 (1976). 4^{4}4R. J. Le Roy, Comp. Phys. Comm. 52, 383 (1989).

ast^{\ast}astThis research was supported by the U.S. National Science Foundation.Author Institution: ... more $^{\ast}$This research was supported by the U.S. National Science Foundation.Author Institution: Department of Chemistry, Michigan State UniversityApproximately 120 pure quadrupole transitions in more than 6 vibrational states in CF,1 have been observed by means of an infrared-radio-frequency double resonance spectrometer operating near 1075cm−11075 cm^{-1}1075cm−1. Double-resonance spectra were observed for five 12C14O2^{12}C^{14}O_{2}12C14O2 and three 12C15O2^{12}C^{15}O_{2}12C15O2 laser lines. The radio frequency source was a 1-500 MHz computer-controlled frequency synthesizer. Although preliminary spectra were recorded with an intra-cavity coaxial cell, the best spectra were obtained with an extra-cavity cell of stripline design. The quadrupole hyperfine structure was calculated by direct diagonalization of the energy matrices. Quadrupole coupling constants obtained for the ground and several excited vibrational states will be compared with previous results obtained by other spectroscopic techniques

Computational and Theoretical Chemistry, 2021

1^{1}1 This research was supported by the U.S. National Science Foundation. Address of Fawzy and ... more $^{1}$ This research was supported by the U.S. National Science Foundation. Address of Fawzy and Schwendeman: Department of Chemistry, Michigan State University, East Lansing, MI 48824.

Author Institution: Department of Chemistry, East Tennessee State University, Johnson City, TN 37... more Author Institution: Department of Chemistry, East Tennessee State University, Johnson City, TN 37504; Department of Chemistry, Emory University, Atlanta, GA 30322

Author Institution: Optical Technology Division, National Institute of Standards and Technology; ... more Author Institution: Optical Technology Division, National Institute of Standards and Technology; Faculty of Science, University of United Arab Emirates

Author Institution: Optical Technology Division, National Institute of Standards and Technology; ... more Author Institution: Optical Technology Division, National Institute of Standards and Technology; University of United Arab Emirates, Faculty of Science; Department of Chemistry, Wesleyan University

Proceedings of the 71st International Symposium on Molecular Spectroscopy, 2016

The Journal of Chemical Physics, 2013

This work reports the first highly correlated ab initio study of the intermolecular and intramole... more This work reports the first highly correlated ab initio study of the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O(2)(-)(X(2)Π(g))-HF(X(1)Σ(+)) complex. Accurate electronic structure calculations were performed using the coupled cluster method including single and double excitations with addition of the perturbative triples correction [CCSD(T)] with the Dunning's correlation consistent basis sets aug-cc-pVnZ, n = 2-5. Also, the explicitly correlated CCSD(T)-F12a level of theory was employed with the AVnZ basis as well as the Peterson and co-workers VnZ-F12 basis sets with n = 2 and 3. Results of all levels of calculations predicted two equivalent minimum energy structures of planar geometry and C(s) symmetry along the A" surface of the complex, whereas the A' surface is repulsive. Values of the geometrical parameters and the counterpoise corrected dissociation energies (Cp-D(e)) that were calculated using the CCSD(T)-F12a/VnZ-F12 level of theory are in excellent agreement with those obtained from the CCSD(T)/aug-cc-pV5Z calculations. The minimum energy structure is characterized by a very short hydrogen bond of length of 1.328 Å, with elongation of the HF bond distance in the complex by 0.133 Å, and D(e) value of 32.313 Kcal/mol. Mulliken atomic charges showed that 65% of the negative charge is localized on the hydrogen bonded end of the superoxide radical and the HF unit becomes considerably polarized in the complex. These results suggest that the hydrogen bond is an incipient ionic bond. Exploration of the potential energy surface confirmed the identified minimum and provided support for vibrationally induced intramolecular proton transfer within the complex. The T-shaped geometry that possesses C(2v) symmetry presents a saddle point on the top of the barrier to the in-plane bending of the hydrogen above and below the axis that connects centers of masses of the monomers. The height of this barrier is 7.257 Kcal/mol, which is higher in energy than the hydrogen bending frequency by 909.2 cm(-1). The calculated harmonic oscillator vibrational frequencies showed that the H-F stretch vibrational transition in the complex is redshifted by 2564 cm(-1) and gained significant intensity (by at least a factor of 30) with respect to the transition in the HF monomer. These results make the O(2)(-)-HF complex an excellent prototype for infrared spectroscopic investigations on open-shell complexes with vibrationally induced proton transfer.

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The Journal of Chemical Physics, 2009

This work presents the first high level correlated ab initio study of the intermolecular potentia... more This work presents the first high level correlated ab initio study of the intermolecular potential energy surface of the ground electronic state of the O(2) (X (3)Sigma(g)(-))-H(2)(X) complex. This computational study was carried out using the CCSD(T) level of theory with the aug-cc-pVXZ basis sets, where X = D, T, Q, and 5. All calculated energies were corrected using the BSSE method. The lowest energy geometry and the shape of the intermolecular potential energy surface showed significant dependence on the size of the basis set as well as the BSSE corrections. The most accurate results were obtained using the CCSD(T)/aug-cc-pVQZ and CCSD(T)/aug-cc-pV5Z combinations with the BSSE corrections. These calculations yield a global minimum of C(2v) symmetry, where internuclear axes of the O(2) and H(2) moieties are parallel to each other. For this geometry, the D(e) value is 65.27(30) cm(-1), which is in excellent agreement with the CBS limit of 65.14 cm(-1). The distance between centers of masses of the H(2) and O(2) monomers within the complex is 3.225(1) A. Barrier heights to rotation of the H(2) and O(2) units by 180 degrees about the axis that connects their centers of masses are 24 and 159 cm(-1), respectively. The current results should stimulate microwave spectroscopic detection of the O(2)-H(2) complex.

The Journal of Chemical Physics, 2005

The H¢-NH(£) van der Waals complex has been examined using ab initio theory and detected via fluo... more The H¢-NH(£) van der Waals complex has been examined using ab initio theory and detected via fluorescence excitation spectroscopy of the