Predissociation lifetimes of vibrational levels of the excited 1B1 (Ka’=0) electronic states of Cd⋅H2 and Cd⋅D2 complexes (original) (raw)
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The outcome of laser excitation of the van der Waals CdH, complex [which consists of a ground-state Cd ('S) atom bound to an H, molecule] to its lowest-energy singlet state(s), which connects with Cd('P) + H, , is examined by calculating a& initio potential-energy surfaces for the above excited singlet states, the corresponding underlying triplet states [connecting to Cd(3P> + H, 1, and the singlet ground state. It is necessary to study such a multitude of states because energetically accessible reaction products such as Cd('P> + H,, CdH(X '2 +) + H, Cd + H + H, and HCdH (X '8:) connect to various surfaces. In carrying out these calculations, the lowest-energy surface of 'A, symmetry was evaluated at nearly 1100 C,, geometries using complete-active-space self-consistent-field wave functions with a valence double-zeta and a double-zeta-plus-polarization basis set on cadmium and hydrogen, respectively. The excited singlet and triplet surfaces that correlate with 'P, and 3PJ levels of Cd plus ground-state H, were examined in detail along paths that flux prepared by laser excitation of the singlet surface(s) is most likely to follow. Among the photoexcited singlet states, the 'B, surface is found to provide the most energetically attractive approach path for the excited CdHl van der Waals complex to access geometries from which HCdH, Cd + H + H, and CdH + H can be formed via intersection and coupling with the lowest 'A, surface. The 'B, surface is found to be weakly attractive, and the excited 'A I surface to be repulsive at geometries characteristic of the nascent photoexcited species. The underlying triplet surfaces are found to be repulsive (3A I), weakly attractive (3B1), and slightly more attractive ("B,) at such geometries. The repulsive 3A r surface intersects the 'B, surface in the latter's entrance-channel "streambed"; the 3B1 state intersects the 'B, surface closer to where the 'B, and lowest 'A, cross. The 3A I and 'B, surfaces also intersect in the entrance streambed of the latter. All such triplet-singlet crossings provide paths to Cd(3P> + H, .
The Journal of Chemical Physics, 2003
Full-dimensional ab initio potential energy surface ͑PES͒ and dipole moment surface ͑DMS͒ are reported for H 5 O 2 ϩ . Tens of thousands of coupled-cluster ͓CCSD͑T͔͒ and second-order Møller-Plesset ͑MP2͒ calculations of electronic energies, using aug-cc-pVTZ basis, were done. The energies were fit very precisely in terms of all the internuclear distances, using standard least-square procedures, however, with a fitting basis that satisfies permutational symmetry with respect to like atoms. The H 5 O 2 ϩ PES is a fit to 48 189 CCSD͑T͒ energies, containing 7962 polynomial coefficients. The PES has a rms fitting error of 34.9 cm Ϫ1 for the entire data set up to 110 000 cm Ϫ1 . This surface can describe various internal floppy motions, including the H atom exchanges, monomer inversions, and monomer torsions. First-and higher-order saddle points have been located on the surface and compared with available previous theoretical work. In addition, the PES dissociates correctly ͑and symmetrically͒ to H 2 OϩH 3 O ϩ , with D e ϭ11 923.8 cm Ϫ1 . Geometrical and vibrational properties of the monomer fragments are presented. The corresponding global DMS fit ͑MP2 based͒ involves 3844 polynomial coefficients and also dissociates correctly.
H + CD 4 Abstraction Reaction Dynamics: Excitation Function and Angular Distributions †
The Journal of Physical Chemistry A, 2006
We compare experimental photoloc measurements and quasi-classical trajectory calculations of the integral cross sections, lab-frame speed distributions, and angular distributions associated with the CD 3 products of the H + CD 4 (ν ) 0) f CD 3 + HD reaction at collision energies ranging from 0.5 to 3.0 eV. Of the potential energy surfaces (PES) we explored, the direct dynamics calculations using the B3LYP/6-31G** density functional theory PES provide the best agreement with the experimental measurements. This agreement is likely due to the better overall description that B3LYP provides for geometries well removed from the minimum energy path, even though its barrier height is low by ∼0.2 eV. In contrast to previous theoretical calculations, the angular distributions on this surface show behavior associated with a stripping mechanism, even at collision energies only ∼0.1 eV above the reaction barrier. Other potential energy surfaces, which include an analytical potential energy surface from Espinosa-García and a direct dynamics calculation based on the MSINDO semiempirical Hamiltonian, are less accurate and predict more rebound dynamics at these energies than is observed. Reparametrization of the MSINDO surface, though yielding better agreement with the experiment, is not sufficient to capture the observed dynamics. The differences between these surfaces are interpreted using an analysis of the opacity functions, where we find that the wider cone of acceptance on the B3LYP surface plays a crucial role in determining the integral cross sections and angular distributions.
Core-excited resonances in the dissociative recombination of CH^{+} and CD^{+}
Physical Review A, 2000
Storage-ring measurements of the dissociative recombination cross section of CD ϩ and CH ϩ molecular ions have revealed prominent resonances at low energy. They were assigned tentatively to capture into core-excited bound Rydberg states, electronically coupled both to the electronic initial continuum and to the dissociative final channel. We present here the result of calculations based on the multichannel quantum defect theory, using molecular data ͑quantum defects and electronic couplings͒ extracted from ab initio structure computations. In addition to the Rydberg states converging to the initial ground state X 1 ⌺ ϩ of the ion, we calculated Rydberg series converging to the first two excited electronic states a 3 ⌸ and A 1 ⌸. The cross section convoluted with the experimental anisotropic Maxwell distribution presents a resonant structure very close to the experimental one, when the ion is assumed to be initially in the lowest rovibrational level of the ground state. We can thus assign the resonances observed near 0.3 and 0.9 eV to low vibrational levels of the 2 ⌸ coreexcited Rydberg states (a 3 ⌸)5s and (A 1 ⌸)3p, respectively. We also give a theoretical estimate of the branching ratio for dissociation to various asymptotic limits, obtained by solving coupled equations for the nuclear wave functions of interacting 2 ⌸ states of CH.
Journal of Molecular Spectroscopy, 2007
A method of supersonic free-jet expansion beam combined with techniques of laser spectroscopy was used in investigation of vibrational and rotational structures in the 1 0 þ u ð5 1 P 1 Þ and 1 1 u (5 1 P 1 ) electronic energy states of Cd 2 . Laser induced fluorescence (LIF) excitation and dispersed fluorescence spectra recorded at the 1 0 þ u À X 1 0 þ g and 1 1 u À X 1 0 þ g transitions provided spectroscopic characteristics of the excited and ground states as well as a shape of the repulsive part of the ground-state potential energy curve (PEC). Rotational structures of the 228 Cd 2 isotopomer recorded in the (t 0 ,t 00 ) = (45,0) and (38,0) bands of the 1 0 þ u X 1 0 þ g and 1 1 u X 1 0 þ g transitions, respectively, were used for a direct determination of the ground-and excited-state bond lengths. Moreover, the 1 1 u -state interatomic potential was obtained numerically using an inverted perturbation approach (IPA). The position and height of the 1 1 u -state potential barrier was determined and compared with results of ab initio calculation. Analysis of Condon-internal-diffraction (CID) profiles in the bound-free dispersed fluorescence spectrum resulted in determination of a degree of repulsion between two ground-state Cd atoms in the dimer, supporting a hypothesis of a covalent admixture to the dominant van der Waals (vdW) bonding.
International Reviews in Physical Chemistry, 2017
A critical review of experimental studies and ab initio calculations of the low-lying ungerade excited and ground state interatomic potentials of Cd 2 van der Waals dimer is presented. Consistency as well as discrepancies between experimental results and ab initio calculations are probed. In order to obtain better agreement with existing experimental data, fill in gaps in current knowledge and provide a unifying framework, advanced all-electron ab initio calculations were performed and simulations of the reported spectra were executed. From simulations of laser-induced fluorescence excitation and dispersed emission spectra, analytical and/or pointwise representations of the A
H + CD 4 Abstraction Reaction Dynamics: Product Energy Partitioning †
The Journal of Physical Chemistry A, 2006
This paper presents experimental and theoretical studies of the product energy partitioning associated with the H + CD 4 (ν ) 0) f HD + CD 3 reaction for the collision energy range 0.5-3.0 eV. The theoretical results are based on quasiclassical trajectories from (1) first principles direct dynamics calculations (B3LYP/ 6-31G**), (2) an empirical surface developed by Espinosa-García [J. Chem. Phys. 2002, 116, 10664] (EG), and (3) two semiempirical surfaces (MSINDO and reparametrized MSINDO). We find that most of the energy appears in product translation at energies just above the reactive threshold; however, HD vibration and rotation become quite important at energies above 1 eV, each accounting for over 20% of the available energy above 1.5 eV, according to the B3LYP calculations. The barrier on the B3LYP surface, though being later than that on EG, predicts significantly higher HD vibrational excitation than EG. This deviation is contradictory to what would be expected on the basis of the Polanyi rules and derives from modest differences in the potential energy surfaces. The CD 3 internal energy is generally quite low, and we present detailed rotational state distributions which show that the CD 3 rotational distribution is largely independent of collision energy in the 0.75-1.95 eV range. The most populated rotational levels are N ) 5 and 6 on B3LYP, with most of that excitation being associated with motion about the C 2 axes, rather than C 3 axis, of the CD 3 product, in good agreement with the experimental results. Through our extensive studies in this and previous work concerning the scattering dynamics, we conclude that B3LYP/6-31G
Electronic spectroscopy of the A1A" - X1A' system of CDBr
We report fluorescence excitation and single vibronic level emission spectra of jet-cooled CDBr in the 450-750 nm region. A total of 32 cold bands involving the pure bending levels 2 0 n with n =3-10 and combination bands 2 0 n 3 0 1 ͑n =2-10͒, 2 0 n 3 0 2 ͑n =2-9͒, 1 0 1 2 0 n ͑n =7-10͒, and 1 0 1 2 0 n 3 0 1 ͑n =6,8-9͒ in the à 1 AЉ ← X 1 AЈ system of this carbene were observed; most of these are reported and/or rotationally analyzed here for the first time. Rotational analysis yielded band origins and effective ͑B ͒ rotational constants for both bromine isotopomers ͑CD 79 Br and CD 81 Br͒. The derived à 1 AЉ vibrational intervals are combined with results of Yu et al. ͓J. Chem. Phys. 115, 5433 ͑2001͔͒
Physical Review A
We investigate the parity (P) and time-reversal (T) symmetry violating effects in the CdH molecule and perform the relativistic coupled-cluster calculation of the molecular parameters-E eff , Ws and WM related to the electric dipole moment of electron (eEDM) interaction, the scalarpseudoscalar (S-PS) nucleus-electron neutral current coupling and the nuclear magnetic quadrupole moment (MQM) interaction with electrons, respectively. We also compute the molecular dipole moment and the magnetic hyperfine structure coupling constant of CdH. The value of E eff , Ws and WM obtained by us in the said molecule are 12.2 GV/cm, 14.0 kHz and 0.82×10 33 Hz/e cm 2 , respectively, with an uncertainty of 10%. Furthermore, we study the trend of electron-correlation in the computed properties of CdH and that of the P, T-odd parameters in the group-12 monohydrides (i.e., ZnH, CdH, and HgH).
Journal of Molecular Structure: THEOCHEM, 1991
The possibility of using the approximate MRSD-CI potential in ab initio calculations of deuteron quadrupole coupling constants of rovibrational levels of HD and D2 in their X11: and B' 1,' states is explored. It is shown that the ensuing approximate treatment of vibrational displacement of the molecules does not prevent the method from describing correctly the main features of the deuteron quadrupole coupling in the low-lying rovibrational levels of these systems. Some aspects for the future use of approximate potentials in the calculation of quadrupole coupling constants are outlined.