The structure of adenine monohydrates studied by femtosecond multiphoton ionization detected IR spectroscopy and quantum chemical calculations

We present femtosecond multiphoton ionization detected infrared spectra of jet-cooled monohydrates of adenine and 9-methyladenine. By quantum chemical vibrational analysis and comparison with available literature data we identified two isomers of adenine hydrate with one water molecule hydrogen-bonded to either the amino or the N9-H group. These two monohydrates revealed different fragmentation patterns in the ion depletion spectra, indicating isomer specific intermolecular dynamics. This different behaviour is discussed in terms of competing electronically excited state relaxation and dissociation processes.