Visible Light-Driven Chemistry of Oxalic Acid in Solid Argon, Probed by Raman Spectroscopy

Abstract

High-overtone induced chemistry of oxalic acid (OA) isolated in a low-temperature argon matrix was investigated using Raman spectroscopy. The Raman spectra of three conformers of OA are presented and discussed. Upon excitation of high overtone combination bands by 532 nm irradiation of the lowest energy cTc structure, the isomerization and unimolecular decomposition of OA were observed. Dissociation was induced presumably by absorption into the 5A(g) + B(u) vibrational state of the OH stretching mode of cTc. The photodecomposition leads to the formation of CO, CO(2), and H(2)O products. The experimental observations were supported by computational studies and vibrational anharmonic calculations.

High vibrational overtone excitation‐induced conformational isomerization of glycolic acid in solid argon matrix

“…Now, we can estimate the rate constant k i = I ( λ ) × σ ( λ ) × ϕ ( λ ) for the isomerization processes. If the quantum yield is set to 0.1, then n k i ~ 3 × 10 −3 s −1 , which is two orders of magnitude larger than the observed reactions constants and the same order of magnitude than the rate constant of high overtone isomerization of formic acid . There is a couple of possible explanations for the smaller observed rate constant.…”

“…The cross section of the sixth CH overtone band can be roughly estimated at two orders of magnitude smaller than that the OH cross sections. One more possible high overtone excitation channel is the high combination mode overtone excitation, which is suggested to drive the overtone‐induced chemistry of oxalic acid in an argon matrix …”

“…We successfully combined Raman spectroscopy and matrix isolation technique to investigate high vibrational excitation‐induced chemistry of the small matrix isolated carboxylic acid molecules . The high overtone excitation of the 6 ← 0 vibrational transition of the OH stretching mode of the trans formic acid in an argon matrix is followed by isomerization to the unstable cis form .…”

“…[27] The high overtone excitation of the combination modes is demonstrated in the case of oxalic acid in an argon matrix, where the overtone combination band excitation of the OH stretching mode is followed by the unimolecular decomposition and isomerization reactions. [28] In this paper, we present the Raman spectrum and the high overtone excitation driven conformational isomerization processes of glycolic acid in a low temperature argon matrix. The high overtone excitation is generated by visible light (532 nm), which energy is high enough to excite the vibrational 6 ← 0 transition of the OH stretching mode.…”

Domino Tunneling

“…6a−c,7,13,21 Most importantly, our FPA work yields 9.7(1) and 10.4(1) kcal mol −1 for the 1tTt → 1cTt (TS1) and 1cTt → 1cTc (TS2) isomerization barriers, respectively, which corrects much higher values of 12.9 (TS1) and 14.8 kcal mol −1 (TS2) reported earlier. 7,13,21 Because the tunneling probability is proportional to a function of the exponential of the square root of the barrier height, 2 the tunneling half-life (t 1/2 ) of 1 was severely overestimated by the computations in ref 13, which predicted t 1/2 to be ca. 19 orders of magnitude longer than that of formic acid, 12q for which t 1/2 is a few minutes.…”