Core-electron excitation and fragmentation processes of hydrogen bonded acetic-acid clusters in the oxygen K-edge region

Abstract

In order to examine inner-shell electron excitation and induced chemical processes of hydrogen-bonded (HB) molecular clusters, time-of-flight (TOF) fragment-mass and excitation spectra of deuterium-labeled acetic-acid-d (AAD) have been studied under the effusive and cluster beam conditions. With O1s(CO) → π* CO excitation at 532 eV, the TOF spectra of AAD clusters were compared with those of the free molecule. Transient intensity-enhancement of CH 3 +/CH 3CO + fragments and growth of mixed-cluster cations, M n D +/M n CH 3CO + could be ascertained in the cluster beams, where AAD molecule is denoted by M. Cluster-specific excitation spectra have been generated by monitoring partial-ion-yields of the mixed-cluster cations. Resonance transitions of O1s(CO/OH) → π* CO were found to shift in energy by +0.37/−0.92 eV upon cluster formation. The production of M n D + can be attributed to a low-energy pathway of deuteron (proton) transfer following fast electronic decays within the clusters made up of a stable dimer-unit with doubly-bridged HBs. The CH 3 +/CH 3CO + intensity variation in beam stagnation pressure clearly shows that a local-fragmentation mechanism as previously proposed is also applicable to the fragmentation processes of the small AAD clusters.