Formic acid dimers in a nitrogen matrix

Abstract

Formic acid (HCOOH) dimers are studied by infrared spectroscopy in a nitrogen matrix and by ab initio calculations. We benefit from the use of a nitrogen matrix where the lifetime of the higher-energy (cis) conformer is very long (∼11 h vs. 7 min in an argon matrix). As a result, in a nitrogen matrix, a large proportion of the cis conformer can be produced by vibrational excitation of the lower-energy (trans) conformer. Three trans-trans, four trans-cis, and three cis-cis dimers are found in the experiments. The spectroscopic information on most of these dimers is enriched compared to the previous studies in an argon matrix. The cis-cis dimers of ordinary formic acid (without deuteration) are reported here for the first time. Several conformational processes are obtained using selective excitation by infrared light, some of them also for the first time. In particular, we report on the formation of cis-cis dimers upon vibrational excitation of trans-cis dimers. Tunneling decays of several dimers have been detected in the dark. The tunneling decay of cis-cis dimers of formic acid as well as the stabilization of cis units in cis-cis dimers is also observed for the first time.

Concerted Pair Motion Due to Double Hydrogen Bonding: The Formic Acid Dimer Case

“…Both are of interest for a rigorous comparison between electronic structure theory and experiment. The alternative cooling mechanism by rare gas matrix isolation [16][17][18][19][20][21][22] introduces characteristic matrix embedding shifts on the order of 1-4% for FAD pair modes in Ar 19 , which also complicate the comparison to theory 23,24 .…”

Reactivity of formic acid (HCOOH) with H atoms on cold surfaces of interstellar interest

“…Recently, Favre et al (2018) reported the first detection of HCOOH towards the TW Hydrae protoplanetatry disk. The observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have shown the trans-HCOOH 6(1,6)-5(1,5) transition at 129 GHz for the lower energy formic acid conformer (Lopes et al 2018), and the measurements revealed a disk-average gas phase trans-HCOOH column density of 2-4 × 10 12 cm −2 , as large as that of methanol CH 3 OH. Cis and trans-HCOOH planar isomer conformers refer to the relative position of the two H atoms in the molecule with respect to C-O bond (Szymafiski & Gillan 1996;Lopes et al 2018).…”

“…The observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have shown the trans-HCOOH 6(1,6)-5(1,5) transition at 129 GHz for the lower energy formic acid conformer (Lopes et al 2018), and the measurements revealed a disk-average gas phase trans-HCOOH column density of 2-4 × 10 12 cm −2 , as large as that of methanol CH 3 OH. Cis and trans-HCOOH planar isomer conformers refer to the relative position of the two H atoms in the molecule with respect to C-O bond (Szymafiski & Gillan 1996;Lopes et al 2018). The radioastronomical observations acquired with the IRAM 30 m telescope revealed the detection of HCOOH even in the comet C/2013R1 (Lovejoy) of planetary system (Makochekanwa et al 2014).…”

“…Pure HCOOH ice as well as HCOOH-H 2 O and HCOOH-CH 3 OH ice matrices have been widely characterized by infrared spectroscopy in previous works (Bisschop et al 2007a;Bennett et al 2011). Whereas HCOOH dimers and their different cis and trans conformers were recently studied experimentally by infrared spectroscopy in nitrogen matrix, and theoretically by abinitio calculations (Lopes et al 2018). The heat of dimerization of formic acid by FTIR, reported in an early work (Henderson 1987) is ∆H D = (−48.0 ± 0.4) kJ mol −1 .…”

Electron Attachment and Electron Ionization of Formic Acid Clusters Embedded in Helium Nanodroplets

“…The FA dimer is a prototype for double bonded cyclic complexes; it has been studied extensively [ 5 – 7 ]. Infrared absorption spectra of FA clusters in noble gas matrices show that FA 3 are chain-like [ 8 ], consistent with its polar character revealed in a molecular beam study utilizing an inhomogeneous electric field [ 9 ].…”