title: Double ionization and Coulomb explosion of the formic acid dimer by intense near-infrared femtosecond laser pulses.
abstract: Ionization and fragmentation of formic acid dimers (HCOOH)(2) and (DCOOD)(2) by irradiation of femtosecond laser pulses (100 fs, 800 nm, ~1 × 10(14) W/cm(2)) were investigated by time-of-flight (TOF) mass spectrometry. In the TOF spectra, we observed fragment ions (HCOOH)H(+), (HCOOH)HCOO(+), and H(3)O(+), which were produced via the dissociative ionization of (HCOOH)(2). In addition, we found that the TOF signals of COO(+), HCOO(+), and HCOOH(+) have small but clear side peaks, indicating fragmentation with large kinetic energy release caused by Coulomb explosion. On the basis of the momentum matching among pairs of the side peaks, a Coulomb explosion pathway of the dimer dication, (HCOOH)(2)(2+) → HCOOH(+) + HCOOH(+), was identified with the total kinetic energy release of 3.6 eV. Quantum chemical calculations for energies of (HCOOH)(2)(2+) were also performed, and the kinetic energy release of the metastable dication was estimated to be 3.40 eV, showing good agreement with the observation. COO(+) and HCOO(+) signals with kinetic energies of 1.4 eV were tentatively assigned to be fragment ions through Coulomb explosion occurring after the elimination of a hydrogen atom or molecule from (HCOOH)(2)(2+). The present observation demonstrated that the formic acid dimer could be doubly ionized prior to hydrogen bond breaking by intense femtosecond laser fields.
authors.affiliation: Faculty of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences, 265-1, Higashijima, Akiha-ku, Niigata-city 956-8603, Japan. hoshina@nupals.ac.jp
authors.forename: Kennosuke
authors.initials: K
authors.lastname: Hoshina
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hagihara
authors.forename: Masashi
authors.initials: M
authors.lastname: Tsuge
mesh_terms: D019281:Dimerization; D005561:Formates / Q000737:chemistry*; D007834:Lasers; D013058:Mass Spectrometry; D011789:Quantum Theory; D013997:Time Factors
chemical_list: D005561:Formates; C030544:formic acid