Collisions of excited Na atoms with H/sub 2/ molecules. I. Ab initio potential energy surfaces and qualitative discussion of the quenching process
Potential energy surfaces have been calculated for the four lowest electronic states of Na (3 /sup 2/S, 3 /sup 2/P)+H/sub 2/(/sup 1/..sigma../sup +//sub g/) by means of the RHF--SCF and PNO--CEPA methods. For the so-called quenching process of Na (3 /sup 2/P) by H/sub 2/ at low initial translational energies (E--VRT energy transfer) the energetically most favorable path occurs in C/sub 2v/ symmetry, since: at intermediate Na--H/sub 2/ separation: the A /sup 2/B/sub 2/ potential energy surface is attractive. From the CEPA calculations, the crossing point of minimal energy between the X /sup 2/A/sub 1/ and A /sup 2/B/sub 2/ surfaces is obtained at R/sub c/ = 3.57 a.u. and r/sub c/ = 2.17 a.u. with an energy difference to the asymptotic limit (R = infinity, r = r/sub e/) of -0.06 eV. It is thus classically accessible without any initial translational energy, but at low initial translational energies (approx.0.1 eV) quenching will be efficient only for arrangements of collision partners close to C/sub 2v/ symmetry. There is little indication of an avoiding crossing with an ionic intermediate correlating asymptotically with Na/sup +/ and H/sub 2//sup -/ as was assumed in previous discussions of the quenching process. The dependence of the total quenching cross sections on the initial translational energy is discussed by means of the ''absorbing sphere'' model, taking the initial zero-point vibrational energy of the hydrogen molecule into account. New experimental data of the product channel distribution in H/sub 2/ for center-of-mass forward scattering are presented. The final vibrational states v' = 3, 2, 1, and 0 of H/sub 2/ are populated to about 26%, 61%, 13%, and 0%, respectively. The observed distributions in H/sub 2/ (and D/sub 2/) may be rationalized by simple dynamic considerations on the basis of the calculated surfaces.
- Research Organization:
- Fachbereich Chemie der Universitaet Kaiserslautern, D-6750 Kaiserslautern, Federal Republic of Germany
- OSTI ID:
- 6168312
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 75:11
- Country of Publication:
- United States
- Language:
- English
Similar Records
Ab initio dynamics: HeH$sup +$ + H$sub 2$ $Yields$ He + H$sub 3$$sup +$ (C$sub 2$/subv/) classical trajectories using a quantum mechanical potential-energy surface
STUDY OF THE REACTION DYNAMICS OF Li + HF, HCl BY THE CROSSED MOLECULAR BEAMS METHOD
Related Subjects
HYDROGEN
ATOM-MOLECULE COLLISIONS
SODIUM
ENERGY TRANSFER
POTENTIAL ENERGY
RADIATIONLESS DECAY
VIBRATIONAL STATES
ALKALI METALS
ATOM COLLISIONS
COLLISIONS
DE-EXCITATION
ELEMENTS
ENERGY
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
METALS
MOLECULE COLLISIONS
NONMETALS
640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena