Temperature effect on the deactivation of electronically excited potassium by hydrogen molecule
Journal
Journal of Chemical Physics
Journal Volume
113
Journal Issue
11
Pages
4613-4619
Date Issued
2000
Author(s)
Hsiao, Y.-C.
Liu, D.-K.
Fung, H.-S.
KING-CHUEN LIN
Abstract
Time-resolved fluorescences from varied K excited states are monitored as a function of H2 pressure. According to a three-level model, the rate coefficients of collisional deactivation for the K 6 2S, 7 2S, and 8 2S states at 473 K have been determined to be 4.94±0.15, 5.30±0.15, and 5.44±0.15×10−9 cm3 molecule−1 s−1. In addition, the collision transfer of S2−D2 transition may be derived to be 5.03±0.21, 4.68±0.30, and 4.89±0.36×10−9 cm3 molecule−1 s−1, showing dominance of the S2-state deactivation processes owing to the effect of near-resonance energy transfer. As the temperature is varied, the activation energies for the collisions of K(6 2S), K(7 2S), and K(8 2S) atoms with H2, respectively, may be estimated to be 5.38±0.33, 4.39±0.16, and 3.23±0.19 kJ/mol. The first two values are roughly consistent with the theoretical calculations of 3.1 and 0.9 kJ/mol in C∞v symmetry predicted by Rossi and Pascale. The obtained energy barriers are small enough to allow for occurrence of the harpoon mechanism, a model applicable to the reactions between H2 and alkali atoms such as K, Rb, and Cs. Among them, K–H2 collisions appear to be the first case to possess a slight energy barrier. This finding of energy barrier may account for the discrepancy for the state reactivity towards H2 observed between K (or Rb) and Cs atoms.
SDGs
Type
journal article