Infrared photodissociation spectroscopic and theoretical study of H n C4O+ (n = 1, 2) cation clusters in the gas phase

Abstract

The carbon chain cations H n C4O+ (n = 1, 2) were generated via pulsed laser vaporisation of a graphite target in supersonic expansions of helium seeded with carbon monoxide and acetylene. The infrared spectra were measured via mass-selected infrared photodissociation spectroscopy of their CO-tagged complexes [H n C4O·CO]+ (n = 1, 2). Their geometric and electronic structures were determined by gas-phase infrared photodissociation spectra combined with theoretical calculations. The results show that the H n C4O+ (n = 1, 2) core cations are linear carbon chain derivatives which are terminated with hydrogen/dihydrogen and oxygen atoms. The HC4O+ cation has 3Σ− electronic ground state with cumulene-like carbon chain structure, while H2C4O+ cation has 2B1 electronic ground state with polyyne-like carbon chain structure. The CH and CH2 terminal groups have different influence on the type of carbon-carbon bonds in the carbon chain derivatives, due to the sp and sp2 hybridisation property. The carbon chain cations H n C4O+ (n = 1, 2) are studied by gas-phase infrared photodissociation spectra of CO-tagged complexes [H n C4O·CO]+ (n = 1, 2) combined with theoretical calculations. Studies show that the structures of the H n C4O+ (n = 1, 2) core cations are linear carbon chain derivatives which are terminated with hydrogen/dihydrogen and oxygen atoms. The spectrum of [HC4O·CO]+ shows two bands above 3000 cm−1, suggesting possible isomers.