Time-resolved molecular chemiluminescence from reactions of Ca(3 P,1 D) atoms with N2O

Abstract

Chemiluminescence from electronically excited CaO generated by reaction of metastable Ca(4s4p(3 P J )) and Ca(4s3d(1 D 2)) atoms with N2O is investigated in the time-resolved mode under bulk conditions. By monitoring molecular emission from some 41 transitions, the time dependence of chemiluminescence from excited CaO states is compared with that for decay of emission from the atomic precursor states from which they are derived, enabling formation of specific product states to be ascribed to either direct generation from chemical reaction between Ca(3 P) and Ca(1 D) atoms with N2O or to an energy transfer mechanism involving the metastable atoms and long-lived dark states of CaO. The different routes leading to specific molecular states are found to be in accord with simple energetic considerations and correlation rules governing the conservation of spin and spatial symmetry. Measurements of vibrational temperatures in one particular product state, CaO(A′1II), indicate some degree of vibrational excitation accompanying these processes. Relative populations in all emitting states of CaO are found to be in agreement with the results of molecular beam experiments. In addition to the study of electronic chemiluminescence from CaO, effective secondorder quenching rate constants are determined for collisional removal of Ca(3 P) and Ca(1 D) atoms via all available physical and chemical pathways. Measurements over a wide range of temperature lead to estimates of activation energies for quenching of both Ca states by N2O.