Probing rotational relaxation in HBr (v=1) using double resonance spectroscopy.

Rotational energy transfer in HBr(v=1)+HBr collisions has been investigated using an optical pump-probe double resonance technique at ambient temperature. Rotationally state selective excitation of v=1 for rotational levels in the range J=0-9 was achieved by stimulated Raman pumping, and the evolution of population was monitored using (2+1) resonantly enhanced multiphoton ionization spectroscopy of the g (3) summation (-)-X (1) summation (+)(0-1) band. Collision-induced population transfer events with DeltaJ<or=8 were observed at a pressure of 0.32 Torr. State-to-field rate constants for loss of population from the initially prepared states ranged from 8.3x10(-10) to 4.9x10(-10) cm(3) s(-1). The full state-to-state rate constant set was analyzed by fitting to numerical solutions of the coupled differential equations describing the relaxation processes. Rate constant matrices were generated using fitting and scaling functions. The rate coefficients were best represented by the statistical power exponential gap law.