Ionization-induced solvent migration in acetanilide-methanol clusters inferred from isomer-selective infrared spectroscopy

摘要

We present the resonance-enhanced multiphoton ionization, infrared-ultraviolet hole burning (IR-UV HB), and IR dip spectra of the trans-acetanilide-methanol (AA-MeOH) cluster in the S_0, S _1, and cationic ground state (D_0) in a supersonic jet. The IR-UV HB spectra demonstrate the co-existence of two isomers in S _(0,1), in which MeOH binds either to the NH or the CO site of the peptide linkage in AA, denoted as AA(NH)-MeOH and AA(CO)-MeOH. When AA(CO)-MeOH is selectively ionized, its IR spectrum in D_0 is the same as that measured for AA~+(NH)-MeOH. Thus, photoionization of AA(CO)-MeOH induces migration of MeOH from the CO to the NH site with 100% yield.