Laser emission from CO formed in the flash-initiated reactions of O(3P) atoms with CS and CSe

Abstract

A study has been made of the laser emission from vibrationally excited CO (CO) formed in the reactions: O(³P)+ CS → CO + S + 356 kJ mol^–1(1) and O(³P)+ CSe → CO + Se +∼494 kJ mol^–1, (5), with O atoms being produced directly by flash photolysis of SO₂. Comparison of the emission from CS₂+ SO₂ with that from CS₂+ O₂ established (a) that excitation and quenching of SO₂ can lead to appreciable heating and as a result lower gains, and (b) that relaxation of CS^†, before it reacts, by SO₂ and free S atoms modifies the laser output significantly. The rise in temperature can be moderated by addition of inert gas or SF₆, but the latter must be used with care as it also relaxes the higher levels of CO^† efficiently. Oscillation has been observed on all vibrational transitions from (20, 19) to (9, 8) with mixtures containing CSe₂ and SO₂; the delay times before individual transitions appeared are consistent with the CO vibrational distribution predicted from infra-red chemiluminescence experiments. The absence of lower transitions is probably due to relaxation in the processes CO(v)+ Se(³P₂)→ CO(v– 1)+ Se(³P₁)(7) which are close to resonance when v∼7.

Once care was taken to minimise the effects of gas heating, the overall outputs from the three lasers, i.e., CS₂+ O₂, CS₂+ SO₂ and CSe₂+ SO₂, were roughly comparable.