Potential energy surface and rovibrational energy levels of the H2-CS van der Waals complex

Inelastic vibrational dynamics of CS in collision with H2 using a full-dimensional potential energy surface

We report a six-dimensional (6D) potential energy surface (PES) for the CS-H2 system computed using high-level electronic structure theory and fitted using a hybrid invariant polynomial method. Full-dimensional quantum close-coupling scattering calculations have been carried out using this potential for rotational and, for the first time, vibrational quenching transitions of CS induced by H2. State-to-state cross sections and rate coefficients for rotational transitions in CS from rotational levels j1 = 0-5 in the ground vibrational state are compared with previous theoretical results obtained using a rigid-rotor approximation. For vibrational quenching, state-to-state and total cross sections and rate coefficients were calculated for the vibrational transitions in CS(v1 = 1,j1) + H2(v2 = 0,j2) → CS(v1' = 0,j1') + H2(v2' = 0,j2') collisions, for j1 = 0-5. Cross sections for collision energies in the range 1 to 3000 cm-1 and rate coefficients in the temperature range of 5 to 600 K are obtained for both para-H2 (j2 = 0) and ortho-H2 (j2 = 1) collision partners. Application of the computed results in astrophysics is also discussed.

Rotational relaxation of CS by collision with ortho- and para-H2 molecules

Quantum mechanical investigation of the rotationally inelastic collisions of CS with ortho- and para-H2 molecules is reported. The new global four-dimensional potential energy surface presented in our recent work is used. Close coupling scattering calculations are performed in the rigid rotor approximation for ortho- and para-H2 colliding with CS in the j = 0-15 rotational levels and for collision energies ranging from 10(-2) to 10(3) cm(-1). The cross sections and rate coefficients for selected rotational transitions of CS are compared with the ones previously reported for the collision of CS with He. The largest discrepancies are observed at low collision energy, below 1 cm(-1). Above 10 cm(-1), the approximation using the square root of the relative mass of the colliders to calculate the cross sections between a molecule and H2 from the data available with (4)He is found to be a good qualitative approximation. The rate coefficients calculated with the electron gas model for the He-CS system show more discrepancy with our accurate results. However, scaling up these rates by a factor of 2 gives a qualitative agreement.