Electronic Spectra of Isoelectronic Amides, Acids, and Acyl Fluorides

The first four bands in the gas-phase spectra of amides, carboxylic acids, and acyl fluorides are thought to be n → π*, n → 3s Rydberg, π → π*, and n → 3p Rydberg excitations. That the second and fourth bands are Rydberg, whereas the first and third are valence shell is demonstrated in a comparison of gas-phase and condensed-phase absorption and circular dichroism spectra. All-electron, SCF Gaussian orbital calculations are also presented which qualitatively explain the trends in the spectra of HCOX molecules, and predict several quantities of interest, such as upper-state dipole moments and magnetic transition moments, which have not been measured as yet.