Structural Rearrangement by Isomer-Specific Infrared Excitation in the Neutral Isolated Dihydrated Cluster of 3-Hydroxyflavone.

Isomer-specific, IR-induced reactions in the electronic ground state (S0) can be of great interest to control reaction pathways. Here we show a first example of these reactions with isomer-specific excitation and formation of a new isomer under isolated conditions in a molecular beam experiment. The investigated dihydrated cluster of 3-hydroxyflavone forms two isomers, I and D, in the S0 state. We show that only a mode-specific excitation of isomer I leads to a structural rearrangement yielding an isomer that has not been identified so far. This isomer is assigned in comparison to quantum chemical calculations. The experiments are performed by applying an IR/IR method in combination with a mass-selective resonant two-photon ionization (R2PI) process. Usually these kinds of IR/IR/R2PI methods are chosen to discriminate isomers; here it is demonstrated that this powerful method can also be applied for analysis of IR-induced reactions probed by an IR/R2PI process.