The formation of mercury molecules

Mercury molecules in the vapour state have never been directly detected. The ratio of the specific heats and vapour density determinations all show that mercury vapour is strictly monatomic, so that so far as chemical evidence is concerned mercury vapour molecules do not exist. However, the occurrence of quite strong hands in the absorption and emission spectra of mercury vapour at high pressure demand the presence of molecules in considerable number. We have obtained definite evidence that diatomic molecules are formed in mercury vapour by the attachment of excited atoms to normal atoms. The formation of the molecules in this way clearly reconciles the chemical evidence of their non-existence with Ike hand spectra evidence of their presence; for, unless the atoms are excited by light or electron impact, the vapour may remain practically monatomic.