COUPLED EMISSION-ABSORPTION SPECTROSCOPY OF ELECTRONIC STATES $CL_{2}$ MOLECULES.

Abstract

Spectroscopy of electronic states of diatomic halogens is of great interest due to its motivation for understanding the kinetics and mechanism of elementary processes of photochemical and chemiluminescent reactions which take place in gases and plasma. In the present work we report results of spectroscopic studies of low-lying electronic states (ES) of $Cl_{2}$ molecules obtained under the thermal heating in shock waves and under the adiabatic cooling in supersonic flow conditions. We were used the probing He-Cd laser source with wavelengths of 441.6 and 325.0nm for the differential absorption spectral analysis and a set of calibrated optical analyzers of "interference filter+photomultiplayer" type as well as OSA instrumentation. At least two signals of the spectral gas absorptivity in UV continuum and two signals of the chemiluminescent gas emissivity in visible and near IR were measured In the assumption of correctness of the Beer law and on the base of known temperature dependencies of the UV absorption coefficients and chemiluminescent rate constants, all state parameters $Cl_{2}$ populations of absorptive ground ES $Cl_{2}(X)$ as well as radiative excited ESs $Cl_{2}(B)$ and $Cl_{2}(A)$, vibrational temperature $T_{v}$, thermodynamic temperature T and concentration of atoms CI were defined. By means of solving the inverse spectroscopic problem, taking into consideration the apparatus curtailment and using accurate RKR potential energy functions and Frank-Condon factors, for the measured $Cl_{2}$ emission in visible and near IR spectrum, the average values of dipole moments for the unbound-bound A-X and bound-bound B-X radiative elctronic transitions were found. Then accounting the contribution of all ro-vibronic transitions, the radiative lifetimes for the lowest vibrational levels of $Cl_{2}(B)$ ES was refined. Moreover, by means of solving the inverse kinetic problems, using accurate time-depending gasdynamic and multi-level kinetic modeling, from the measured $CL_{2} ES$ parameters, a set of important kinetic characterstics such as radiative recombination efficiency, electronic quenching rate constants, vibrational relaxation time, etc.was determined.