Collisional deactivation of singlet methylene in the photolysis of ketene

An investigation has been made into the effect of inert gas additions on product quantum yields for the photolysis at 2800 and 2490 Å of mixtures of ketene and oxygen and for the photolysis at 2800 Å of mixtures of ketene and carbon monoxide. Concentration ratios of O 2 (or CO) to CH 2 CO were chosen so that the reaction of CH 2 ( 3 Σ g − ) with CH 2 CO could be ignored and C 2 H 4 formation could be attributed entirely to the reaction[Formula: see text]Quenching of the C 2 H 4 quantum yield by inert gases was interpreted in terms of collisional deactivation of CH 2 ( 1 A 1 ) to the ground state[Formula: see text]and rate constant ratios k 2 /k 1 have been determined for a number of gases: He (0.018), Ar (0.014), Kr (0.033), Xe (0.074), N 2 (0.052), N 2 O (0.10), CF 4 (0.047), C 2 F 6 (0.11), and SF 6 (0.045). It has been assumed that collision-induced intersystem crossover in excited singlet ketene makes an insignificant contribution to the observed quenching effects, but it has not been possible to verify this assumption experimentally. The mechanism of collision-induced electronic relaxation of singlet methylene is discussed in the light of the results.