Ionization-induced conformational changes: REMPI and ZEKE spectroscopy of salicyl and benzyl alcohol

Salicyl and benzyl alcohol have been studied using (1+1′) resonance-enhanced multiphoton ionization (REMPI) spectroscopy to investigate the conformation adopted by a flexible CH2OH group in the presence and absence of an intramolecular hydrogen bond. The salicyl acid spectrum shows extensive progressions and combinations of CH2OH bending and torsional motions, indicating that a considerable geometry change occurs upon S1←S0 excitation, in contrast to benzyl alcohol which shows relatively little vibrational excitation. Zero electron kinetic energy (ZEKE) spectra of the alcohols display very weak ionization thresholds and no resolved vibrational features, indicating that substantial conformational changes occur upon ionization. Ab initio calculations are presented to support these conclusions.