Hydration of a cationic amide group: a ZEKE spectroscopic study of trans-formanilide–H2OElectronic supplementary information (ESI) available: Ab initio CASSCF/cc-pVDZ geometry parameters of t-FA–H2ONH in the S0, S1 and D0 states (Table S1), CASSCF/cc-pVDZ charges of t-FA–H2ONH in the S0, S1 and D0 states (Table S2), CASSCF/cc-pVDZ harmonic frequencies for the S0, S1 and D0 of t-FA–H2ONH up to 1000 cm–1

Abstract

The gas-phase structures of the two isomers (N–H⋯OH2 bonded and CO⋯HOH bonded) of the trans-formanilide–water complex have been investigated by two-colour (1 + 1′) resonance enhanced multiphoton ionisation (REMPI) and zero electron kinetic energy (ZEKE) spectroscopy. Excitation energies were determined for the S1 00 transitions of trans-formanilide–water to be 35 787 ± 0.2 cm−1 (NH-bound) and 36 118 ± 0.2 cm−1 (CO-bound) which correspond to a red shift of 218 cm−1 and a blue shift of 114 cm−1, respectively. This is in excellent agreement with recent one-colour measurements of Dickinson et al., J. Chem. Phys. A, 1999, 103, 6938; and Fedorov et al., J. Chem. Phys. A, 2000, 104, 4943. The D0 00 origins of NH-bound and CO-bound trans-formanilide–water were observed by ZEKE spectroscopy at 64 225 ± 5 cm−1 and 64 230 ± 20 cm−1 corresponding to red shifts of 3182 cm−1 and 3177 cm−1, respectively. Both the REMPI and the ZEKE spectra show numerous intermolecular transitions which were assigned on the basis of comparison to similar complexes and to the trans-formanilide monomer. To support these assignments, ZEKE spectra of trans-formanilide–water (NH-bound) were recorded via several vibrationally excited S1 intermediate states, and ab initio CASSCF calculations were also performed.