Abstract
We have used time-resolved IR emission spectroscopy to examine collision induced intersystem crossing (CIISC) and deactivation of vibronically excited cis-HCCO(ã4A″), generated following the 193nm photolysis of ethyl ethynyl ether, by inert gases: He, Ar, and Xe. Observation of vibrationally excited CO(X1Σ+), in experiments quenched with Ar or Xe, suggest rapid CIISC due to a heavy-atom effect. Conversely, experiments quenched with He show transient signal from cis-HCCO(ã4A″), and a distinct absence of CO(X1Σ+), suggesting that CIISC occurs only after cis-HCCO(ã4A″) has been quenched (i.e., CIISC is significantly less efficient with He). Inert gas CIISC rate constants for cis-HCCO(ã4A″) were deduced to be kISCHe=(4.3±0.2)×10−11cm3molecules-1s-1, kISCAr=(8.1±0.2)×10−11cm3molecules-1s-1, and kISCXe=(13.0±0.1)×10−11cm3molecules-1s-1. Additionally, we report the first experimental assignment of 1785±36cm−1 for the fundamental transition of the ν2 asym-CCO stretch of cis-HCCO(ã4A″), which, compared with ab initio calculations, suggests that cis-HCCO(ã4A″) exhibits positive anharmonicity.
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