Molecular size effect on the site-specific fragmentation of N and O K shell excited CH3OCOCN and CH3OCOCH2CN molecules

Abstract

The effect of molecular size on the site-specific fragmentation was investigated by exciting the N and O K shells of methyl cyanoformate (CH3OCOCN) and methyl cyanoacetate (CH3OCOCH2CN). The fragmentation patterns were essentially identical in the N and O core excitations of CH3OCOCN. Site and state dependent fragmentation was clearly observed in the core hole CH3OCOCH2CN: The fragment ions mainly observed at the O K edge excitation were CH3+, HCO+, CH2CN+, CH3OCO+, and COCH2CN+. At the N(1s) excitation the large CH3OCO+ and COCH2CN+ fragments were extremely depressed, and alternatively the small CH3+, HCO+, and CH2CN+ ions were dominant. Especially at the π*CN←N(1s) resonance transition the N+ and CO+ fragment ions were exclusively produced with yields of 40 and 15%, respectively. The total photoabsorption cross sections were measured in the N and O K regions and the observed peaks were tentatively assigned. Reflectron type time-of-flight mass spectrometry was employed to attain the mass separation M/ΔM≥100 at M/e≈100 for the core excited molecules ejecting fragments with considerable kinetic energies.