The Formic Acid Cluster Distribution Observed with Femtosecond Laser Ionization

Microsolvation studies have begun to shed the light on the impact that single water molecules have on the structure of a molecule. The difference in behavior that molecules show when exposed to an increasing number of water molecules has been considered important but remains elusive. The cluster distributions of formic acid were studied for its known importance as an intermediate in the water gas shift reaction. Implementations of the water gas shift reaction range from a wide range of applications. Studies have proposed implementations such as variety such as making water on the manned mission to mars and as an industrial energy source. The reaction pathway of formic acid favors decarboxylation in solvated conditions but control over the pathway is an important field of study. Formic acid was introduced into a high vacuum system in the form of a cluster beam via supersonic expansion and was ionized with the second harmonic (400nm) of a pump-probe laser. Mass spectra showed a ‘magic’ 5,1 (formic acid, water) peak which showed higher intensity than was usually observed in clusters with 1 water molecule. Peak integration showed a higher relative abundance for the 5,1 cluster as well and showed the increased binding favorability of this conformation. As a result, there is an enhanced probability of molecules sticking together in this arrangement and this is due to the stable, cage-like structure that the formic acid forms when surrounding the water molecule.