title: Inner-shell excitation spectroscopy and fragmentation of small hydrogen-bonded clusters of formic acid after core excitations at the oxygen K edge.
abstract: Inner-shell excitation spectra and fragmentation of small clusters of formic acid have been studied in the oxygen K-edge region by time-of-flight fragment mass spectroscopy. In addition to several fragment cations smaller than the parent molecule, we have identified the production of HCOOH.H+ and H3O+ cations characteristic of proton transfer reactions within the clusters. Cluster-specific excitation spectra have been generated by monitoring the partial ion yields of the product cations. Resonance transitions of O1s(C[double bond]O/OH) electrons into pi(CO)* orbital in the preedge region were found to shift in energy upon clusterization. A blueshift of the O1s(C[double bond]O)-->pi(CO)* transition by approximately 0.2 eV and a redshift of the O1s(OH)-->pi(CO)* by approximately 0.6 eV were observed, indicative of strong hydrogen-bond formation within the clusters. The results have been compared with a recent theoretical calculation, which supports the conclusion that the formic-acid clusters consist of the most stable cyclic dimer andor trimer units. Specifically labeled formic acid-d, HCOOD, was also used to examine the core-excited fragmentation mechanisms. These deuterium-labeled experiments showed that HDO+ was formed via site-specific migration of a formyl hydrogen within an individual molecule, and that HD2O+ was produced via the subsequent transfer of a deuterium atom from the hydroxyl group of a nearest-neighbor molecule within a cationic cluster. Deuteron (proton) transfer from the hydroxyl site of a hydrogen-bond partner was also found to take place, producing deuteronated HCOOD.D+ (protonated HCOOH.H+) cations within the clusters.
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan. tabayasi@sci.hiroshima-u.ac.jp
authors.forename: Kiyohiko
authors.initials: K
authors.lastname: Tabayashi
authors.forename: Keisuke
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Osamu
authors.initials: O
authors.lastname: Takahashi
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tamenori
authors.forename: James R
authors.initials: JR
authors.lastname: Harries
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Gejo
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Iseda
authors.forename: Takashi
authors.initials: T
authors.lastname: Tamura
authors.forename: Kenji
authors.initials: K
authors.lastname: Honma
authors.forename: Isao H
authors.initials: IH
authors.lastname: Suzuki
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Nagaoka
authors.forename: Toshio
authors.initials: T
authors.lastname: Ibuki