REMPI spectroscopy of internal state populations in HBr+Ar free jets: Rotational relaxation of HBr

The (2 + 1) resonance enhanced multiphoton ionization spectra of HBr were obtained through the E(1)Sigma(+) state for HBr seeded in Ar free jets. Analysis of the two-photon absorption line strength factors allowed determination of quantitative populations for the HBr rotational manifold. A study of the terminal HBr rotational state distributions was made for a wide variety of p(0)D values of the jets. These nonequilibrium population distributions were then modeled by numerical solutions of the set of coupled kinetic equations describing the rotationally inelastic collisions with the buffer. Using a power-law relaxation model, the j-j' rotationally state specific relaxation cross-sections and rate coefficients were determined as a function of temperature over the range present in the post-continuum zone of the free jet flows (180 to 15 K). (C) 1998 Elsevier Science B.V. All rights reserved.