An investigation of the H g ( 6 3 P l t C 0 system by physical measurements (emission, pressure studies) relevant to the reported Hg*CO species have yielded no additional evidence of its formation.Chemical experiments on the decomposition of ethylene and H z are in accord with formation of a long lived (> s) species. The relative quenching rate constants of the species by CzH4, Hz, and C O are 1:0.10-0.18:0.023, respectively.The reliability of the "carbon monoxide effect" as a criterion for distinguishing the nature of the quenching process is discussed in the light of a CO enhancement effect (-30%) observed in the Hg (63Pl) photosensitized decomposition OF hydrogen in the presence of CO and at conditions of incomplete quenching. An alternative to Hg*CO excimer formation is also discussed. This approach is based on the possible formation of Hg(63Po) atoms in quantities in excess of those currently accepted, when Hg-CO mixtures are irradiated with 2537 Pi light.

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