Vibronic absorption spectra of phenyl alkyne cations in solid argon at 20 K

Abstract

Phenyl alkyne samples at high dilution in argon were subjected to argon resonance radiation during condensation at 20 K. Sharp band origins at 579.0 and 586.0 nm agree with the differences between sharp first and fourth photoelectron bands for phenyl acetylene and 1-phenyl-1-propyne, which identifies the molecular cation absorptions. Vibronic assignments are supported by isotopic substitution and comparison to spectra of phenyl acetylene. Substitutent vibrations dominate the red transition, which is predominantly π(ring) ← π(alkyne), whereas ring vibrations dominate the UV transition for 1-phenyl-1-propyne, which is localized on the aromatic ring.