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

Salicyl and benzyl alcohol have been studied using (1 + 1') resonance-enhan ced multiphoton ionization (REMPI) spectroscopy to investigate the conforma tion adopted by a flexible CH2OH group in the presence and absence of an in tramolecular hydrogen bond. The salicyl acid spectrum shows extensive progr essions and combinations of CH2OH bending and torsional motions, indicating that a considerable geometry change occurs upon S-1 <-- S-0 excitation, in contrast to benzyl alcohol which shows relatively little vibrational excit ation. Zero electron kinetic energy (ZEKE) spectra of the alcohols display very weak ionization thresholds and no resolved vibrational features, indic ating that substantial conformational changes occur upon ionization. Ab ini tio calculations are presented to support these conclusions. (C) 2000 Elsev ier Science B.V. All rights reserved.