X-Ray photoelectron spectrum of methylisocyanide gas

The C and N 1s spectra of methylisocyanide gas have been recorded. Two resolvable peaks of equal intensity are observed in the C 1s spectrum. Using the equivalent-cores approximation and thermochemical data, together with MNDO MO calculations and the point-charge potential model, the lower-binding-energy C 1s line is assigned to photo-emission from the isocyano carbon. The strong satellites which have been observed in the spectra of coordination complexes of alkyl and aryl isocyanides are not observed in the spectra of the free molecule. Comparisons of the point-charge-potential-corrected binding energies for C 1s and N 1s photoemissions from CH₃NC and its isomer CH₃CN with those for a host of other molecules show that photoemissions from the internal atoms in these molecules are accompanied by substantially less than average relaxation energies. These smaller relaxation energies can be understood using valence-bond theory.