Higher energy electronic transitions of HC2n+1H+ (n=2–7) and HC2n+1H (n=4–7) in neon matrices

Electronic absorption spectra of linear HC2n+1H+ (n=2–7) were recorded in 6 K neon matrices following their mass-selective deposition. Four new electronic band systems are identified; the strongest ˜E Π2g/u←˜X Π2u/g lies in the UV and the second most intense ˜C Π2g/u←˜X Π2u/g is located in the visible range. The known ˜A Π2g/u←˜X Π2u/g absorption is an order of magnitude weaker than ˜C Π2g/u←˜X Π2u/g. Transitions to the ˜B and ˜D states are also discussed. The wavelengths of the HC2n+1H+ (n=2–7) electronic systems obey a linear relation as a function of the size of the cations, similar to other carbon chains. The ˜B Σu−3←˜X Σg−3 transition in the UV of neutral HC2n+1H (n=4–7) has also been identified upon photobleaching of the cations trapped in the matrices.