Abstract
We present a joint experimental and theoretical study of the VUV-induced dynamics of ${\mathrm{H}}_{2}\mathrm{O}$ and its deuterated isotopologues in the first excited state ($\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{A}{\phantom{\rule{0.28em}{0ex}}}^{1}{B}_{1}$) utilizing a VUV-pump VUV-probe scheme combined with $ab$ initio classical trajectory calculations. 16-fs VUV pulses centered at 161 nm created by fifth-order harmonic generation are employed for single-shot pump-probe measurements. Combined with a precise determination of the VUV pulses' temporal profile, they provide the necessary temporal resolution to elucidate sub-10-fs dissociation dynamics in the 1+1 photon ionization time window. Ionization with a single VUV photon complements established strong-field ionization schemes by disclosing the molecular dynamics under perturbative conditions. Kinetic isotope effects derived from the pump-probe experiment are found to be in agreement with our by ab initio classical trajectory calculations, taking into account photoionization cross sections for the ground and first excited state of the water cation.
Highlights
The VUV-induced photodissociation reaction of water via the first excited state (A 1B1) has been the subject of an abundance of theoretical and experimental studies, as a prototype for a repulsive, barrierless, adiabatic dissociation reaction
We present a joint experimental and theoretical study of the VUV-induced dynamics of H2O and its deuterated isotopologues in the first excited state (A 1B1) utilizing a VUV-pump VUV-probe scheme combined with ab initio classical trajectory calculations. 16-fs VUV pulses centered at 161 nm created by fifth-order harmonic generation are employed for single-shot pump-probe measurements
To analyze reaction dynamics on this short time scale, a detailed knowledge of the instrument response function, which is given by the second-order intensity autocorrelation (IAC), is necessary
Summary
The VUV-induced photodissociation reaction of water via the first excited state (A 1B1) has been the subject of an abundance of theoretical and experimental studies, as a prototype for a repulsive, barrierless, adiabatic dissociation reaction. The potential energy surface [1,2] of the first excited state has been calculated with high precision by Staemmler and Palma [1] This is a widely utilized calculation and has been further improved by different groups [3,4,5]. Based on these calculations, previous theoretical studies focused on the interpretation of the A 1B1 absorption spectrum [6,7,8,9], as well as on the rotational fine structure of the dissociation products [10]. Farmanara et al [20,21] were able to identify an upper bound of 20 fs for the photodissociation time constant in the A 1B1 state, limited by their temporal resolution in a 155-nm single-color pump-probe
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