Cross sections and rate constants for low-temperature $sup 4$He--H$sub 2$ vibrational relaxation
Converged coupled-states integral cross sections were determined for the vibrational relaxation of the v=1 j=0 level of p-H$sub 2$ in collisions with $sup 4$He. The collision energies ranged from 0.005 to 0.4 eV. The Gordon--Secrest (GS) potential was used with both a harmonic (HO) and rotating-Morse oscillator (MO) description of the H$sub 2$ molecule. Additional calculations incorporated modifications in the long-range and spherically symmetric (V$sub 0$) parts of the purely repulsive GS surface. Rotational coupling plays a major role in vibrational relaxation even at thermal energies. Although the relative importance of individual vibration--rotation transitions is a sensitive function of the choice of intramolecular potential, the HO and MO total relaxation cross sections are nearly identical. These total relaxation cross sections exhibit a power-law dependence on the initial translational energy down to approx.0.1 eV above threshold; below which point a positive curvature appears for all the surfaces considered. Rate constants for vibrational relaxation were computed and compared with experiment for 60 degreeK <500 degreeK. The GS rates lie below the experimental values and exhibit a less pronounced curvature at low temperatures. Introducing the correct long-range attraction into the GS V$sub 0$ potential results in a modest increase in curvature. Agreement with experiment is obtained only with the use of the semiempirical V$sub 0$ potential of Shafer and Gordon. (AIP)
- Research Organization:
- Department of Chemistry, University of Maryland, College Park, Maryland 20742
- NSA Number:
- NSA-33-021204
- OSTI ID:
- 4071300
- Journal Information:
- J. Chem. Phys., v. 64, no. 2, pp. 452-459, Other Information: Orig. Receipt Date: 30-JUN-76
- Country of Publication:
- United States
- Language:
- English
Similar Records
Chemical reaction versus vibrational quenching in low energy collisions of vibrationally excited OH with O
Rate constants for intermediate and high temperature /sup 4/He--H/sub 2/ and /sup 4/He--D/sub 2/ vibrational relaxation
Related Subjects
N60200 -Physics (Atomic & Molecular)-Atomic & Molecular Properties
640304* -Physics Research-Atomic
Molecular & Chemical Physics-Collision Phenomena
*HELIUM- ATOM-MOLECULE COLLISIONS
*HYDROGEN- ATOM-MOLECULE COLLISIONS
CROSS SECTIONS
DE-EXCITATION
HELIUM 4
MILLI EV RANGE
VIBRATIONAL STATES