Robert Forrey | Penn State University (original) (raw)
Papers by Robert Forrey
The Astrophysical Journal, 1999
We describe quantum-mechanical scattering calculations of ro-vibrational transitions in induced b... more We describe quantum-mechanical scattering calculations of ro-vibrational transitions in induced by H 2 collisions with He. We use a close-coupled description of the dynamics which includes full ro-vibrational coupling and a reliable potential energy surface. Rate coefficients for rotational and vibrational transitions in ortho-and are presented in the temperature range 10 ¹ T ¹ 5000 K. para-H 2
Physical Review A, 2003
The ¤ index of refraction for sodium matter waves traveling in a cold noble-gas medium is calcula... more The ¤ index of refraction for sodium matter waves traveling in a cold noble-gas medium is calculated as a function ¥ of temperature and beam velocity. Resonances and glory oscillations are present in the center-of-mass scattering ¦ amplitude and may be seen in the refractive index at very low temperatures. The sensitivity of the calculations § to the molecular potential is investigated for the case of argon, and results at 300 K are compared tö a recent experiment. Effective range parameters are computed and the attenuation and phase of the matter waves © are analyzed as a function of temperature and beam velocity.
Physical Review A, 2004
... RC Forrey, Phys. Rev. A 66, 023411 (2002). K. Tilford, M. Hoster, P. Florian, and RC Forrey, ... more ... RC Forrey, Phys. Rev. A 66, 023411 (2002). K. Tilford, M. Hoster, P. Florian, and RC Forrey, Phys. Rev. A 69, 052705 (2004). JM Doyle, B. Friedrich, J. Kim, and D. Patterson, Phys. ... H. Rabitz, J. Chem. Phys. 57, 1718 (1972) [INSPEC][CAS]; and, 59, 943 (1973) [INSPEC][CAS]. ...
![Research paper thumbnail of Close-coupling study of rotational energy transfer and differential scattering in H[sub 2]O collisions with He atoms](https://attachments.academia-assets.com/42379045/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2007
Quantum close-coupling scattering calculations of rotational energy transfer in the vibrationally... more Quantum close-coupling scattering calculations of rotational energy transfer in the vibrationally excited CO due to collisions with He atom are presented for collision energies between 10(-5) and approximately 1000 cm-1 with CO being initially in the vibrational level upsilon=2 and rotational levels j=0,1,4, and 6. The He-CO interaction potential of Heijmen et al. [J. Chem. Phys. 107, 9921 (1997)] was adopted for the calculations. Cross sections for rovibrational transitions and state-to-state rotational energy transfer from selected initial rotational levels were computed and compared with recent measurements of Carty et al. [J. Chem. Phys. 121, 4671 (2004)] and available theoretical results. Comparison in all cases is found to be excellent, providing a stringent test for the scattering calculations as well as the reliability of the He-CO interaction potential by Heijmen et al.
The European Physical Journal D, 2004
Rate coefficients for cold and ultracold He+CO collisions are used together with radiative lifeti... more Rate coefficients for cold and ultracold He+CO collisions are used together with radiative lifetimes to investigate the relaxation of rotationally hot polar molecules in the presence of a cold or ultracold helium buffer gas. Starting with an initial Gaussian distribution of highly excited rotational states, such as might be produced by an optical centrifuge, the time-dependent relaxation of a collection of super rotors is studied andin the case of CO an emission spectrum which contains the collisional information is predicted as a function of buffer gas density. Implications for the experimental detection of cold and ultracold quasiresonant atom-diatom scattering is discussed.
Quantum mechanical calculations of collisional quenching cross sections and rate coefficients for... more Quantum mechanical calculations of collisional quenching cross sections and rate coefficients for various internally excited atoms and molecules at cold and ultracold temperatures are presented. The efficiencies of relaxation for vibrationally, rotationally, and electronically excited states are given and in each case the dominant decay mechanisms are discussed.
![Research paper thumbnail of Close-coupling calculations of low-energy inelastic and elastic processes in [sup 4]He collisions with H[sub 2]: A comparative study of two potential energy surfaces](https://attachments.academia-assets.com/42989957/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2005
The two most recently published potential energy surfaces (PESs) for the HeH 2 complex, the so-ca... more The two most recently published potential energy surfaces (PESs) for the HeH 2 complex, the so-called MR (Muchnick and Russek) and BMP (Boothroyd, Martin, and Peterson) surfaces, are quantitatively evaluated and compared through the investigation of atom-diatom collision processes. The BMP surface is expected to be an improvement, approaching chemical accuracy, over all conformations of the PES compared to that of the MR surface. We found significant differences in inelastic rovibrational cross sections computed on the two surfaces for processes dominated by large changes in target rotational angular momentum. In particular, the H 2 (ν = 1, j = 0) total quenching cross section computed using the BMP potential was found to be a factor of 1000 larger than that obtained with the MR surface. A lesser discrepancy persists over a large range of energies from the ultracold to thermal and occurs for other low-lying initial rovibrational levels. The MR surface was used in previous calculations of the H 2 (ν = 1, j = 0) quenching rate coefficient and gave results in close agreement with the experimental data of Audibert et al. which were obtained for temperatures between 50 and 300 K. Examination of the rovibronic coupling matrix elements, that are obtained following a Legendre expansion of the PES, suggests that the magnitude of the anisotropy of the BMP potential is too large in the interaction region. However, cross sections for elastic and pure rotational processes obtained from the two PESs differ typically by less than a factor of two. The small differences may be ascribed to the long-range and anharmonic components of the PESs. Exceptions occur for (ν = 10, j = 0) and (ν = 11, j = 1) where significant enhancements have been found for the low-energy quenching and elastic cross sections due to zero-energy resonances in the BMP PES which are not present in the MR potential.
The Astrophysical Journal, 2008
Rate coefficients for rotational transitions in H 2 induced by H 2 impact are presented. Extensiv... more Rate coefficients for rotational transitions in H 2 induced by H 2 impact are presented. Extensive quantum mechanical coupled-channel calculations based on a recently published (H 2 ) 2 potential energy surface were performed. The potential energy surface used here is presumed to be more reliable than surfaces used in previous work. Rotational transition cross sections with initial levels J ≤ 8 were computed for collision energies ranging between 10 −4 and 2.5 eV, and the corresponding rate coefficients were calculated for the temperature range 2 ≤ T ≤ 10,000 K. In general, agreement with earlier calculations, which were limited to 100-6000 K, is good though discrepancies are found at the lowest and highest temperatures. Low-density-limit cooling functions due to para-and ortho-H 2 collisions are obtained from the collisional rate coefficients. Implications of the new results for non-thermal H 2 rotational distributions in molecular regions are also investigated.
Quantum scattering calculations of H2 + H2, both ortho-para and ortho-ortho cases, and HD + H2 ha... more Quantum scattering calculations of H2 + H2, both ortho-para and ortho-ortho cases, and HD + H2 have been carried out at cold and ultracold temperatures using ab inito potential energy surfaces for the H4 system developed by Hinde and Boothroyd and coworkers. The calculations were performed in the rigid rotor approximation using the MOLSCAT code as well as the vibrating
The H2-H2 system has long been considered as a benchmark candidate for quantum dynamics studies o... more The H2-H2 system has long been considered as a benchmark candidate for quantum dynamics studies of molecule-molecule collisions. H2 is the most abundant molecular species in the interstellar medium and rotational and vibrational transitions in collisions between H2 molecules have been topics of considerable interest. Here, we present a full quantum mechanical treatment of collisions between ortho-ortho, para-para, and ortho-para H2 molecules as well as the HD-H2 system over a wide range of energies and for different initial rovibrational levels of the molecules. The computed rate constants are compared against available experimental data and previous theoretical results.
Contributions to Atomic, Molecular, and Optical Physics, Astrophysics, and Atmospheric Physics - Proceedings of the Dalgarno Celebratory Symposium, 2010
The negative hydrogen ion H− plays an important role in the continuum opacity of late-type stars ... more The negative hydrogen ion H− plays an important role in the continuum opacity of late-type stars and in the kinetics of low-metallicity gas. We review the H− photodetachment cross section along with other processes involving H−. We address H− in early Universe chemistry, the role of oscillator-strength sum-rules in constraining its continuum cross section, and the influence of autodetaching resonances on the efficiency of H− photodestruction in the reionization era. Keywords: atomic processes-early universe- ...
The Journal of Chemical Physics, 2015
A multiconfiguration self-consistent field/molecular dynamics study of the (n→π * ) 1 transition ... more A multiconfiguration self-consistent field/molecular dynamics study of the (n→π * ) 1 transition of carbonyl compounds in liquid water A quantum kinetic theory of molecule formation is presented which includes three-body recombination and radiative association for a thermodynamically closed system which may or may not exchange energy with its surrounding at a constant temperature. The theory uses a Sturmian representation of a two-body continuum to achieve a steady-state solution of a governing master equation which is self-consistent in the sense that detailed balance between all bound and unbound states is rigorously enforced. The role of quasibound states in catalyzing the molecule formation is analyzed in complete detail. The theory is used to make three predictions which differ from conventional kinetic models. These predictions suggest significant modifications may be needed to phenomenological rate constants which are currently in wide use. Implications for models of low and high density systems are discussed. C 2015 AIP Publishing LLC. [http://dx.
Physical Review A, 2004
V ¤ ariational calculations of the ground-state energy of helium are performed using a basis set ... more V ¤ ariational calculations of the ground-state energy of helium are performed using a basis set representation that ¥ includes an explicit treatment of the Fock expansion in hyperspherical coordinates. The construction of basis ¦ functions that have the correct cusp behavior at three-particle coalescence points and the evaluation of integrals containing these functions is discussed. The basis set in hyperspherical coordinates is added to a basis set § consisting of products of Laguerre polynomials in perimetric coordinates. It is demonstrated that the use of Fock basis functions provides a substantial improvement in the convergence rate of the basis set expansion.
Astronomy and Astrophysics
Collisional excitation rate coefficients play an important role in the dynamics of energy transfe... more Collisional excitation rate coefficients play an important role in the dynamics of energy transfer in the interstellar medium. In particular, accurate rotational excitation rates are needed to interpret microwave and infrared observations of the interstellar gas for nonlocal thermodynamic equilibrium line formation. Theoretical cross sections and rate coefficients for collisional deexcitation of rotationally excited HF in the vibrational ground state are reported. The quantum-mechanical close-coupling approach implemented in the nonreactive scattering code MOLSCAT was applied in the cross section and rate coefficient calculations on an accurate 2D HF-He potential energy surface. Estimates of rate coefficients for H and H$_2$ colliders were obtained from the HF-He collisional data with a reduced-potential scaling approach. The calculation of state-to-state rotational quenching cross sections for HF due to He with initial rotational levels up to j=20j=20j=20 were performed for kinetic energ...
Physical Review A
A numerical investigation of the doubly excited states of Hâ converging to the H(n=2)+H(n{sup ... more A numerical investigation of the doubly excited states of Hâ converging to the H(n=2)+H(n{sup '}=2) limit was performed. Special emphasis was put on the accurate description of the range of intermediate internuclear distances in order to correctly connect the short range with the asymptotic van der Waals regime where perturbation theory is applicable. The present nonperturbative calculation extends to internuclear separations R=200aâ and is sufficiently accurate to achieve a connection between the two extreme regimes without any need for an interpolation procedure. The high precision of the ab initio results revealed a long range dipole-quadrupole interaction that had been omitted in two earlier calculations. In addition to revised first-order perturbation theory results the leading second-order term varying as Râ»â¶ was obtained. The impact of the present findings for cold H(n=2) collisions is briefly discussed.
Physical review letters, Jan 7, 2012
Highly efficient and specific energy transfer mechanisms that involve rotation-rotation, vibratio... more Highly efficient and specific energy transfer mechanisms that involve rotation-rotation, vibration-vibration, and vibration-rotation exchange in diatomic molecules are examined theoretically in ultracold H(2), D(2), and HD self-collisions as a function of initial vibrational level v. The three quasiresonant mechanisms are found to operate for all vibrational levels and yield complex scattering lengths which vary smoothly with v. Exceptions to this trend occur at select high values of v where the scattering lengths are modulated by orders of magnitude corresponding to the location of an s-wave zero-energy resonance in "vibration space." The quasiresonant mechanisms, which are not very sensitive to the details of the interaction potential, generally control the final distribution of molecular states for any given initial distribution. The zero-energy resonances are more sensitive to the potential and may be used to vibrationally "tune" the interaction strength, sim...
The Astrophysical Journal, 1999
We describe quantum-mechanical scattering calculations of ro-vibrational transitions in induced b... more We describe quantum-mechanical scattering calculations of ro-vibrational transitions in induced by H 2 collisions with He. We use a close-coupled description of the dynamics which includes full ro-vibrational coupling and a reliable potential energy surface. Rate coefficients for rotational and vibrational transitions in ortho-and are presented in the temperature range 10 ¹ T ¹ 5000 K. para-H 2
Physical Review A, 2003
The ¤ index of refraction for sodium matter waves traveling in a cold noble-gas medium is calcula... more The ¤ index of refraction for sodium matter waves traveling in a cold noble-gas medium is calculated as a function ¥ of temperature and beam velocity. Resonances and glory oscillations are present in the center-of-mass scattering ¦ amplitude and may be seen in the refractive index at very low temperatures. The sensitivity of the calculations § to the molecular potential is investigated for the case of argon, and results at 300 K are compared tö a recent experiment. Effective range parameters are computed and the attenuation and phase of the matter waves © are analyzed as a function of temperature and beam velocity.
Physical Review A, 2004
... RC Forrey, Phys. Rev. A 66, 023411 (2002). K. Tilford, M. Hoster, P. Florian, and RC Forrey, ... more ... RC Forrey, Phys. Rev. A 66, 023411 (2002). K. Tilford, M. Hoster, P. Florian, and RC Forrey, Phys. Rev. A 69, 052705 (2004). JM Doyle, B. Friedrich, J. Kim, and D. Patterson, Phys. ... H. Rabitz, J. Chem. Phys. 57, 1718 (1972) [INSPEC][CAS]; and, 59, 943 (1973) [INSPEC][CAS]. ...
The Journal of Chemical Physics, 2007
Quantum close-coupling scattering calculations of rotational energy transfer in the vibrationally... more Quantum close-coupling scattering calculations of rotational energy transfer in the vibrationally excited CO due to collisions with He atom are presented for collision energies between 10(-5) and approximately 1000 cm-1 with CO being initially in the vibrational level upsilon=2 and rotational levels j=0,1,4, and 6. The He-CO interaction potential of Heijmen et al. [J. Chem. Phys. 107, 9921 (1997)] was adopted for the calculations. Cross sections for rovibrational transitions and state-to-state rotational energy transfer from selected initial rotational levels were computed and compared with recent measurements of Carty et al. [J. Chem. Phys. 121, 4671 (2004)] and available theoretical results. Comparison in all cases is found to be excellent, providing a stringent test for the scattering calculations as well as the reliability of the He-CO interaction potential by Heijmen et al.
The European Physical Journal D, 2004
Rate coefficients for cold and ultracold He+CO collisions are used together with radiative lifeti... more Rate coefficients for cold and ultracold He+CO collisions are used together with radiative lifetimes to investigate the relaxation of rotationally hot polar molecules in the presence of a cold or ultracold helium buffer gas. Starting with an initial Gaussian distribution of highly excited rotational states, such as might be produced by an optical centrifuge, the time-dependent relaxation of a collection of super rotors is studied andin the case of CO an emission spectrum which contains the collisional information is predicted as a function of buffer gas density. Implications for the experimental detection of cold and ultracold quasiresonant atom-diatom scattering is discussed.
Quantum mechanical calculations of collisional quenching cross sections and rate coefficients for... more Quantum mechanical calculations of collisional quenching cross sections and rate coefficients for various internally excited atoms and molecules at cold and ultracold temperatures are presented. The efficiencies of relaxation for vibrationally, rotationally, and electronically excited states are given and in each case the dominant decay mechanisms are discussed.
The Journal of Chemical Physics, 2005
The two most recently published potential energy surfaces (PESs) for the HeH 2 complex, the so-ca... more The two most recently published potential energy surfaces (PESs) for the HeH 2 complex, the so-called MR (Muchnick and Russek) and BMP (Boothroyd, Martin, and Peterson) surfaces, are quantitatively evaluated and compared through the investigation of atom-diatom collision processes. The BMP surface is expected to be an improvement, approaching chemical accuracy, over all conformations of the PES compared to that of the MR surface. We found significant differences in inelastic rovibrational cross sections computed on the two surfaces for processes dominated by large changes in target rotational angular momentum. In particular, the H 2 (ν = 1, j = 0) total quenching cross section computed using the BMP potential was found to be a factor of 1000 larger than that obtained with the MR surface. A lesser discrepancy persists over a large range of energies from the ultracold to thermal and occurs for other low-lying initial rovibrational levels. The MR surface was used in previous calculations of the H 2 (ν = 1, j = 0) quenching rate coefficient and gave results in close agreement with the experimental data of Audibert et al. which were obtained for temperatures between 50 and 300 K. Examination of the rovibronic coupling matrix elements, that are obtained following a Legendre expansion of the PES, suggests that the magnitude of the anisotropy of the BMP potential is too large in the interaction region. However, cross sections for elastic and pure rotational processes obtained from the two PESs differ typically by less than a factor of two. The small differences may be ascribed to the long-range and anharmonic components of the PESs. Exceptions occur for (ν = 10, j = 0) and (ν = 11, j = 1) where significant enhancements have been found for the low-energy quenching and elastic cross sections due to zero-energy resonances in the BMP PES which are not present in the MR potential.
The Astrophysical Journal, 2008
Rate coefficients for rotational transitions in H 2 induced by H 2 impact are presented. Extensiv... more Rate coefficients for rotational transitions in H 2 induced by H 2 impact are presented. Extensive quantum mechanical coupled-channel calculations based on a recently published (H 2 ) 2 potential energy surface were performed. The potential energy surface used here is presumed to be more reliable than surfaces used in previous work. Rotational transition cross sections with initial levels J ≤ 8 were computed for collision energies ranging between 10 −4 and 2.5 eV, and the corresponding rate coefficients were calculated for the temperature range 2 ≤ T ≤ 10,000 K. In general, agreement with earlier calculations, which were limited to 100-6000 K, is good though discrepancies are found at the lowest and highest temperatures. Low-density-limit cooling functions due to para-and ortho-H 2 collisions are obtained from the collisional rate coefficients. Implications of the new results for non-thermal H 2 rotational distributions in molecular regions are also investigated.
Quantum scattering calculations of H2 + H2, both ortho-para and ortho-ortho cases, and HD + H2 ha... more Quantum scattering calculations of H2 + H2, both ortho-para and ortho-ortho cases, and HD + H2 have been carried out at cold and ultracold temperatures using ab inito potential energy surfaces for the H4 system developed by Hinde and Boothroyd and coworkers. The calculations were performed in the rigid rotor approximation using the MOLSCAT code as well as the vibrating
The H2-H2 system has long been considered as a benchmark candidate for quantum dynamics studies o... more The H2-H2 system has long been considered as a benchmark candidate for quantum dynamics studies of molecule-molecule collisions. H2 is the most abundant molecular species in the interstellar medium and rotational and vibrational transitions in collisions between H2 molecules have been topics of considerable interest. Here, we present a full quantum mechanical treatment of collisions between ortho-ortho, para-para, and ortho-para H2 molecules as well as the HD-H2 system over a wide range of energies and for different initial rovibrational levels of the molecules. The computed rate constants are compared against available experimental data and previous theoretical results.
Contributions to Atomic, Molecular, and Optical Physics, Astrophysics, and Atmospheric Physics - Proceedings of the Dalgarno Celebratory Symposium, 2010
The negative hydrogen ion H− plays an important role in the continuum opacity of late-type stars ... more The negative hydrogen ion H− plays an important role in the continuum opacity of late-type stars and in the kinetics of low-metallicity gas. We review the H− photodetachment cross section along with other processes involving H−. We address H− in early Universe chemistry, the role of oscillator-strength sum-rules in constraining its continuum cross section, and the influence of autodetaching resonances on the efficiency of H− photodestruction in the reionization era. Keywords: atomic processes-early universe- ...
The Journal of Chemical Physics, 2015
A multiconfiguration self-consistent field/molecular dynamics study of the (n→π * ) 1 transition ... more A multiconfiguration self-consistent field/molecular dynamics study of the (n→π * ) 1 transition of carbonyl compounds in liquid water A quantum kinetic theory of molecule formation is presented which includes three-body recombination and radiative association for a thermodynamically closed system which may or may not exchange energy with its surrounding at a constant temperature. The theory uses a Sturmian representation of a two-body continuum to achieve a steady-state solution of a governing master equation which is self-consistent in the sense that detailed balance between all bound and unbound states is rigorously enforced. The role of quasibound states in catalyzing the molecule formation is analyzed in complete detail. The theory is used to make three predictions which differ from conventional kinetic models. These predictions suggest significant modifications may be needed to phenomenological rate constants which are currently in wide use. Implications for models of low and high density systems are discussed. C 2015 AIP Publishing LLC. [http://dx.
Physical Review A, 2004
V ¤ ariational calculations of the ground-state energy of helium are performed using a basis set ... more V ¤ ariational calculations of the ground-state energy of helium are performed using a basis set representation that ¥ includes an explicit treatment of the Fock expansion in hyperspherical coordinates. The construction of basis ¦ functions that have the correct cusp behavior at three-particle coalescence points and the evaluation of integrals containing these functions is discussed. The basis set in hyperspherical coordinates is added to a basis set § consisting of products of Laguerre polynomials in perimetric coordinates. It is demonstrated that the use of Fock basis functions provides a substantial improvement in the convergence rate of the basis set expansion.
Astronomy and Astrophysics
Collisional excitation rate coefficients play an important role in the dynamics of energy transfe... more Collisional excitation rate coefficients play an important role in the dynamics of energy transfer in the interstellar medium. In particular, accurate rotational excitation rates are needed to interpret microwave and infrared observations of the interstellar gas for nonlocal thermodynamic equilibrium line formation. Theoretical cross sections and rate coefficients for collisional deexcitation of rotationally excited HF in the vibrational ground state are reported. The quantum-mechanical close-coupling approach implemented in the nonreactive scattering code MOLSCAT was applied in the cross section and rate coefficient calculations on an accurate 2D HF-He potential energy surface. Estimates of rate coefficients for H and H$_2$ colliders were obtained from the HF-He collisional data with a reduced-potential scaling approach. The calculation of state-to-state rotational quenching cross sections for HF due to He with initial rotational levels up to j=20j=20j=20 were performed for kinetic energ...
Physical Review A
A numerical investigation of the doubly excited states of Hâ converging to the H(n=2)+H(n{sup ... more A numerical investigation of the doubly excited states of Hâ converging to the H(n=2)+H(n{sup '}=2) limit was performed. Special emphasis was put on the accurate description of the range of intermediate internuclear distances in order to correctly connect the short range with the asymptotic van der Waals regime where perturbation theory is applicable. The present nonperturbative calculation extends to internuclear separations R=200aâ and is sufficiently accurate to achieve a connection between the two extreme regimes without any need for an interpolation procedure. The high precision of the ab initio results revealed a long range dipole-quadrupole interaction that had been omitted in two earlier calculations. In addition to revised first-order perturbation theory results the leading second-order term varying as Râ»â¶ was obtained. The impact of the present findings for cold H(n=2) collisions is briefly discussed.
Physical review letters, Jan 7, 2012
Highly efficient and specific energy transfer mechanisms that involve rotation-rotation, vibratio... more Highly efficient and specific energy transfer mechanisms that involve rotation-rotation, vibration-vibration, and vibration-rotation exchange in diatomic molecules are examined theoretically in ultracold H(2), D(2), and HD self-collisions as a function of initial vibrational level v. The three quasiresonant mechanisms are found to operate for all vibrational levels and yield complex scattering lengths which vary smoothly with v. Exceptions to this trend occur at select high values of v where the scattering lengths are modulated by orders of magnitude corresponding to the location of an s-wave zero-energy resonance in "vibration space." The quasiresonant mechanisms, which are not very sensitive to the details of the interaction potential, generally control the final distribution of molecular states for any given initial distribution. The zero-energy resonances are more sensitive to the potential and may be used to vibrationally "tune" the interaction strength, sim...