Bending Relaxation of H2O by Collision with Para‐ and Ortho‐H2

• Published in: Chemphyschem Vol. 25; no. 2
• Main Authors: García‐Vázquez, Ricardo Manuel, Faure, Alexandre, Stoecklin, Thierry
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 15-01-2024
• Subjects: Astrochemistry; Bending; Collisional Energy Transfer; Collisions; Coupled modes; Energy transfer; Inelastic Dynamics; Potential energy; Propensity Rules; Quantum Chemistry; Quantum numbers; Rotation; Vibration mode
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.202300698

We extend our recent theoretical work on the bending relaxation of H2O in collisions with H2 by including the three water modes of vibration coupled with rotation, as well as the rotation of H2. Our full quantum close‐coupling method (excluding the H2 vibration) is combined with a high‐accuracy nine‐dimensional potential energy surface. The collisions of para‐H2O and ortho‐H2O with the two spin modifications of H2 are considered and compared for several initial states of H2O. The convergence of the results as a function of the size of the rotational basis set of the two colliders is discussed. In particular, near‐resonant energy transfer between H2O and H2 is found to control the vibrational relaxation process, with a dominant contribution of transitions with
Δj2=j2f-j2i
${{\rm{\Delta }}j_2 = j_2^f - j_2^i }$
=
+2,+4
${ + 2, + 4}$
,
j2i
${j_2^i }$
and
j2f
${j_2^f }$
being respectively the H2 initial and final rotational quantum numbers. Finally, the calculated value of the H2O bending relaxation rate coefficient at 295 K is found to be in excellent agreement with its experimental estimate.
A comparison is made between the vibrational quenching rate coefficients of H2O (ν2=1) due to collisions with the two spin modifications of H2 and the global Boltzmann averaged rate coefficient. Additionally, the sole available experimental value[37] at 295 K is presented. The dynamics reference frame has been incorporated.