Theoretical–Experimental Study of Formic Acid Photofragmentation in the Valence Region

Abstract

Photoionization and photofragmentation studies of formic acid (HCOOH) are performed for the valence shell electron ionization process. The total and partial ion yield of gaseous HCOOH were collected as a function of photon energy in the ultraviolet region, between 11.12 and 19.57 eV. Measurements of the total and partial ion yield of gaseous formic acid molecule are performed with a time-of-flight mass spectrometer at the Synchrotron Light Brazilian Laboratory. Density functional theory and time dependent density functional theory are employed to calculate the ground and excited electronic state energies of neutral and ionic formic acid as well as their fragments and normal vibration modes. The ionization potential energies, the stability of electronic excited states of HCOOH(+), and the energies of opening fragmentation channels are estimated from theoretical-experimental analysis. Additionally, the main formic acid photofragmentation pathways by exposition of photons within that energy range are determined experimentally. These produced ions primarily have the following mass/charge ratios: 46 (HCOOH(+)), 45 (COOH(+)), 29 (HCO(+)), and 18 (H(2)O(+)).

Communication: Protonation process of formic acid from the ionization and fragmentation of dimers induced by synchrotron radiation in the valence region

“…1,10,11,16,17 The explanation found in the literature for these cations is generally due to the presence of the isotope 13 C. In a brief analysis by Leach et al 16 for the case of acetic acid, m/q = 60, it is suggested that the appearance of the ion at m/q = 61 can be due to the presence of an isotope 13 C, to the molecular fragmentation of dimers, or to the fragmentation of a complex formed by water contamination. According to this work, the formation energy of a protonated ion from a dimer would be about 200 meV lower than the ion derived from monomers containing 13 Aim of the present work is to analyze the process of protonation due to the formation of dimers and their influence on the results of molecular ionization and fragmentation pattern at VUV range.…”

Cross Sections and Asymmetry Parameters for Formic Acid in the Vacuum-Ultraviolet Energy Range

“…Threshold photoelectron and photoionization total ion yield spectra were reported by Siggel-King et al in the 11–21 eV range. Finally, the total ion yield and partial ion yield in the range of 12.12–19.57 eV were reported by Arruda et al These authors also report density functional and time-dependent density functional calculations of the ground- and excited-state electronic energies of neutral and ionic formic acid as well as their fragments. Previous theoretical studies also include the investigation of the ionic states observed in the photoelectron spectrum by Takeshita and the calculated VUV absorption spectrum reported by Osted et al…”

Formic Acid Ionization and Fragmentation by Multiphoton Absorption

“…DeWitt [27] have addressed the dependence of dissociation yield with molecular size, however until the present, Keldysh theory is applied. More than 20 different cations were observed corresponding to some dissociation channels already proposed [22]. Spectra were obtained at radiation intensities between 9.25×10 9 and 5×10 10 W/cm 2 , without and with He and Ar as carrier gases.…”

“…Most of the ionic species have been observed in experiments of formic acid destruction by soft X rays [21,22] inner shell excitation [23] ultraviolet region [10] or the interaction with protons or electrons [19,28]. In this work, we analyze the mass spectra of the ions obtained as a result of the interaction between formic acid and laser radiation with different intensities of 532 nm radiation, contrasting them with some of the available theoretical and computational results.…”

“…The intensity of ions with greater masses detected, increased as a function of the laser intensity. Regarding the ion CO 2 H + it is only observed in [22] in dissociation by electrons in [29]. It has not been experimentally reported in other papers.…”