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

• Published in: Journal of electron spectroscopy and related phenomena 2011-04, Vol.184 (3), p.134-139
• Main Authors: Tabayashi, K., Yamamoto, K., Maruyama, T., Yoshida, H., Okada, K., Tamenori, Y., Suzuki, I.H., Gejo, T., Honma, K.
• Format: Article
• Language: English
• Subjects: Acetic-acid clusters; Beams (radiation); Cations; Cluster-band shift; Clusters; Core-level excitation; Electronics; Excitation; Excitation spectra; Fragmentation; Hydrogen bond; TOF spectroscopy
• ISSN: 0368-2048; 1873-2526
• DOI: 10.1016/j.elspec.2010.12.019

▶ Core-electron excitation spectra and fragmentation processes of acetic-acid clusters. ▶ O1s(CO) → π* CO transitions shift by +0.37/−0.92 eV upon cluster formation. ▶ Hydrogen-bond strength of RCOOH clusters determines the cluster-band shift. ▶ We propose “local-fragmentation” and “low-energy M n X + formation” mechanisms. ▶ Fragmentation after electronic relaxation follows either of these two mechanisms. 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.