Resonant desorption of ice with a tunable LiNbO3 optical parametric oscillator

We report on the use of a pulsed tunable mid-infrared optical parametric oscillator (OPO) for the IR resonant desorption of ice in the 3 μm range. Desorbed neutrals are detected by UV multi-photon ionization and time-of-flight mass spectrometry. Desorption yield is found to increase linearly with the OPO pulse energy in the 0–3 mJ range. The resonant character of the desorption process is very clearly evidenced by the study of the wavelength dependency of the desorption yield. The desorption spectrum peaks at 3.1 μm and is in remarkable agreement with the absorption spectrum of crystalline ice at T=100 K. This result differs from previous experiments using NIR macro-pulses of a free electron laser. The velocity distribution of the desorption products reveals the presence of at least two components. The fast component is consistent with our previous results obtained on doped ices and indicates a phase explosion process. The observation of high-n (H3O)+(H2O)n clusters is also reported.