Reaction of Cr atoms with O-2 at low pressures: Observation of new chemiluminescence bands from CrO2

Abstract

Ground and low-lying electronic states of Cr atoms in the gas phase were generated from photolysis of Cr(CO)6 vapor in He or Ar using an unfocussed weak UV laser pulse and their reactions with 02 and NO were studied. When 0.5-1.0 Torr of Cr(CO)(6)/O-2/He or Ar mixtures were photolyzed using 295-300 nm laser pulses, broadband chemiluminescence peaked at similar to420 and similar to500 nm, respectively, was observed in addition to the atomic emissions from z(7)p(o), z(5)P(o), and y(7)p(o) states of Cr atoms. When N2O was used instead of O-2, no chemiluminescence was observed. The chemiluminescence intensities as well as the LIF intensities for those three low-lying electronic states (a(7)S(3), a(5)S(2) and a(5) D-J) showed second-order dependence on the photolysis laser power. Also, the chemiluminescence intensities were first-order in O-2 pressure, but the presence of excess Ar showed a strong inhibition effect on them. Based on the experimental results, the chemiluminecent species in this work is attributed to CrO2* generated from hot ground state Cr atoms with O-2. The apparent radiative lifetimes of the chemiluminescent species and collisional quenching rate constants by O-2 and Ar also were investigated.