Ab initio potential energy surface and rotationally inelastic collisions of LiH (X1Σ+) with H. I. The ab initio evaluation of the potential energy surface (original) (raw)
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… and Theoretical Chemistry, 2012
In this work, the inelastic collision of hydroxide of lithium with argon is studied for a fixed experimental value of the LiH bond length 3.0139 bohr using an ab initio energy surface. The potential energy surface (PES) for the LiH(X 1 R + )-Ar( 1 S) Van der Waals system is calculated accurately at the ab initio coupled-cluster [CCSD(T)] with an aug-cc-pVQZ Gaussian basis set for the H and Ar atoms and cc-pVQZ Gaussian basis set for the Li atom. In this calculation, the basis set superposition error (BSSE) was corrected at all geometries with the counterpoise procedure of Boys and Bernadi. The interaction potential has a global minimum at h = 180°and at an equilibrium distance R = 5.30 bohr with a well depth of 525.13 cm À1 . This potential already fitted analytically and expanded in terms of Legendre polynomials is employed to evaluate the state-to-state rotational cross sections over a range of energies up to 6452.584 cm À1 . The calculations of cross sections are done in the close coupling (CC) approach. The features present on low collision energy some resonances and are related to the anisotropic interaction potential. We have compared the cross sections in LiH-Ar at 6452.584 cm À1 with the available experiment one of Wilcomb and Dagdigian and the earlier calculations of Bhattacharyya et al. However, we have found that the results show a good agreement especially for j = 1 ? 0 transition.
2016
A theoretical study of rotational collision of LiH(X 1 Σ + ,v = 0, J) with Ar has been carried out. The ab initio potential energy surface (PES) describing the interaction between the Ar atom and the rotating LiH molecule has been calculated very accurately and already discussed in our previous work [Computational and Theoretical Chemistry 993 (2012) 20-25]. This PES is employed to evaluate the de-excitation cross sections. The ab initio PES for the LiH (X 1 Σ +)-Ar(1 S) Van der waals system is calculated at the coupled-cluster [CCSD(T)] approximation for a LiH length fixed to an experimental value of 3.0139 bohrs. The basis set superposition error (BSSE) is corrected and the bond functions are placed at mid-distance between the center of mass of LiH and the Ar atom. The cross sections are then derived in the close coupling (CC) approach and rate coefficients are inferred by averaging these cross sections over a Maxwell-Boltzmann distribution of kinetic energies. The 11 first rotational levels of rate coefficients are evaluated for temperatures ranging from 10 to 300 K. We notice that the de-excitation rate coefficients appear large in the order 10 −10 cm −3 s −1 and show very low temperature dependence. The rate coefficients magnify significantly the propensity toward Δ J = −1 transitions. These results confirm the same propensity already noted for the cross sections.
SpringerPlus, 2014
A theoretical study of rotational collision of LiH(X 1 Σ + ,v = 0, J) with Ar has been carried out. The ab initio potential energy surface (PES) describing the interaction between the Ar atom and the rotating LiH molecule has been calculated very accurately and already discussed in our previous work [Computational and Theoretical Chemistry 993 (2012) 20-25]. This PES is employed to evaluate the de-excitation cross sections. The ab initio PES for the LiH (X 1 Σ + )-Ar( 1 S) Van der waals system is calculated at the coupled-cluster [CCSD(T)] approximation for a LiH length fixed to an experimental value of 3.0139 bohrs. The basis set superposition error (BSSE) is corrected and the bond functions are placed at mid-distance between the center of mass of LiH and the Ar atom. The cross sections are then derived in the close coupling (CC) approach and rate coefficients are inferred by averaging these cross sections over a Maxwell-Boltzmann distribution of kinetic energies. The 11 first rotational levels of rate coefficients are evaluated for temperatures ranging from 10 to 300 K. We notice that the de-excitation rate coefficients appear large in the order 10 −10 cm −3 s −1 and show very low temperature dependence. The rate coefficients magnify significantly the propensity toward Δ J = −1 transitions. These results confirm the same propensity already noted for the cross sections.
Journal of Molecular Structure: THEOCHEM, 2004
The potential energy surface describing the interaction between the hydrogen atom and the rotating LiH molecule has been calculated very accurately and presented in our previous work (J. Mol. Struct. (THEOCHEM) 678 (2004) 11). The rigid rotor potential already fitted analytically and expanded in terms of Legendre polynomials, is employed here to evaluate the pure state-to-state rotational cross-sections over a range of energies of astrophysical interest varying from 10 to 3000 cm 21. An exact close coupling and CS calculation of the state to state rotational cross-section was done first in the range of small energy, from 10 to 100 cm 21. The comparison of both results shows the good agreement between them and leads to a generalisation of such calculation for higher energy using the CS approximation. We determine the state to state rotational cross-section for transitions from j ¼ 0; 1, 2, 3, 4 to all accessible final states j 0 ; at total energy varying between 10 and 3000 cm 21. The presented cross-sections were found to be very large even for low energy and large D jj 0 : Thus indicates the important probability to produce the heated LiH molecule in excited states by collisions with H and explain the strong anisotropy discussed in our previous paper.
Journal of Molecular Spectroscopy, 2016
A very accurate dipole moment curve (DMC) for the ground X 1 Σ + electronic state of the 7 LiH molecule is reported. It is calculated with the use of all-particle explicitly correlated Gaussian functions with shifted centers. The DMC-the most accurate to our knowledge-and the corresponding highly accurate potential energy curve are used to calculate the transition energies, the transition dipole moments, and the Einstein coefficients for the rovibrational transitions with ∆J = −1 and ∆v ≤ 5. The importance of the non-adiabatic effects in determining these properties is evaluated using the model of a vibrational R-dependent effective reduced mass in the rovibrational calculations introduced earlier (Diniz et al., Chem. Phys. Lett. 633, 89 (2015)). The results of the present calculations are used to assess the quality of the two complete linelists of 7 LiH available in the literature.
Can the LiH molecule bind He atoms? A computational experiment
Chemical Physics Letters, 1999
One of the most recently computed ab initio potentials for the LiH molecule interacting with an He atom is selected to study the possible existence of weakly bound states between the three particles. Various numerical methods are employed to search for the van der Waals complex. A computational extension to larger clusters with more helium atoms is also examined and the implications which the present results have for the ultracold physics of this system are discussed. q 1999 Elsevier Science B.V. All rights reserved.
Chemical Physics, 1995
All adiabatic curves of LiH + dissociating into Li (2s, 2p, 3s, 3p, 3d) + H + and Li + + H(1 s, 2s, 2p) are determined by an ab initio approach involving a non-empirical pseudopotential for the Li(1 s 2) core and core valence correlation corrections. The resulting spectroscopic constants and vibrational level spacings of all these states are presented. From ~he usual semiclassical approximations an analysis of the high energy vibrational level spacing is performed allowing for accurate long range extrapolations. For the lowest curves dissociating into Li + + H (I s) and Li (2s) + H + an analysis of the main electronic interactions is carded out from adiabatic model and reveals the importance of the binding charge delocalisation effects versus the polarisation (charge localised) ones. In addition the LiH photoelectron spectrum is calculated. An interesting feature of that spectrum is that both bound-bound and bound-free transitions coexist due to the particular shape of the LiH and LiH + potential energy curves.
Revista Mexicana De Fisica, 2010
espanolEn este trabajo estudiamos la influencia del conjunto de bases de orbitales atomicos sobre la determinacion de la curva de energia potencial (CEP) correspondiente al estado fundamental (formula) de la molecula diatomica Hidruro de Litio. La energia electronica del LiH es calculada, en los marcos de la aproximacion Born-Oppenheimer, a nivel ICC usando los conjuntos de funciones base cc-pVXZ (X=D, T and Q). A partir de las CEP calculadas, determinamos los niveles de energia vibracional y respectivas constantes espectroscopicas. Los resultados obtenidos son comparados con valores experimentales y teoricos publicados previamente. EnglishIn this work we stufy the influence of atomic orbital bases sets in the determination of ground state (formule) potential energy curve of Lithium Hydride diatomic molecule. The electronic energies of LiH are calculated, within the Born-Oppenheimer approximation, at the full Configuration Interaction level using cc-pVXZ (X=D, T and Q) basis sets. F...
Chemical Physics Letters, 1990
On the basis of recently published, bond-distance dependent semiempirical potentials total cross sections have been calculated for L&-He and Liz-Kr collisions as functions of collision energy and initial vibrational state y= O-20 of the molecule, using either the vibrational adiabatic quantum-mechanical infinite-order-sudden (10s) approximation or vibration-dependent quasiclassical trajectories (QCT). Via the QCT calculations the experimentally observed non-monotonic change of total cross section with changing initial vibrational state could be reproduced and explained. For Li2( Y)-He at E,,=O.O& eV the vibrational and rotational inelastic cross sections at r.+=20 are significantly larger than for q=O.