IR laser resonant desorption of formaldehyde–H2O ices: hydrated cluster formation and velocity distribution

We report on the use of the IR laser resonant desorption technique to generate long series of organic hydrated clusters (M(H2O)n, with M=HCO+, H3CO+, etc.) from frozen aqueous solutions of formaldehyde. The presence of mixed clusters (M(H2CO)p(H2O)n) has also been identified. The cluster size distribution has been analyzed and the results were discussed with respect to the formaldehyde–water reactions in condensed phase. The velocity distribution of desorbed species has been recorded in order to get better insight on the laser–solid interaction. The velocity profile shows the presence of two distinct components. It is found that the desorption process is described by a phase explosion process, followed by a normal vaporization.