Abstract
The gas phase structure and excited state dynamics of o-aminophenol-H2O complex have been investigated using REMPI, IR-UV hole-burning spectroscopy, and pump-probe experiments with picoseconds laser pulses. The IR-UV spectroscopy indicates that the isomer responsible for the excitation spectrum corresponds to an orientation of the OH bond away from the NH2 group. The water molecule acts as H-bond acceptor of the OH group of the chromophore. The complexation of o-aminophenol with one water molecule induced an enhancement in the excited state lifetime on the band origin. The variation of the excited state lifetime of the complex with the excess energy from 1.4 ± 0.1 ns for the 0-0 band to 0.24 ± 0.3 ns for the band at 0-0 + 120 cm(-1) is very similar to the variation observed in the phenol-NH3 system. This experimental result suggests that the excited state hydrogen transfer reaction is the dominant channel for the non radiative pathway. Indeed, excited state ab initio calculations demonstrate that H transfer leading to the formation of the H3O(•) radical within the complex is the main reactive pathway.
Highlights
It has long been observed that molecules like indole or phenol dissolved in water can be ionized with photon energy as low as 4.5 eV (the Ionization Potential (IP) of bare indole is 8.8 eV).[1,2] Many hypotheses have been presented in the literature concerning the possible mechanism of ionization at such a low energy.[3,4] One possibility, which has been the subject of strong controversy, is the role of the hydronium radical (H3O ) in the first step of the process.[5]
We present experimental results coupled with ab-initio calculations, which demonstrate the role of the H3O radical in the deactivation process of the first excited state of a model system: the ortho-aminophenol-water complex (o-amPhOH-H2O)
We present here a study of the o-amPhOH-H2O complex, combining spectroscopy with nanosecond lasers, excited state lifetime determination by picosecond pump-probe experiments and theoretical calculations in the ground and electronically excited states, which show that the excited state hydrogen transfer (ESHT)
Summary
It has long been observed that molecules like indole or phenol dissolved in water can be ionized with photon energy as low as 4.5 eV (the Ionization Potential (IP) of bare indole is 8.8 eV).[1,2] Many hypotheses have been presented in the literature concerning the possible mechanism of ionization at such a low energy.[3,4] One possibility, which has been the subject of strong controversy, is the role of the hydronium radical (H3O ) in the first step of the process.[5] some ab-initio calculations suggest the formation of this radical,[6-78] there was no direct evidence of this process. We present experimental results coupled with ab-initio calculations, which demonstrate the role of the H3O radical in the deactivation process of the first excited state of a model system: the ortho-aminophenol-water complex (o-amPhOH-H2O)
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