Anion photoelectron imaging spectroscopy of glyoxal

Abstract

We report a photoelectron imaging study of the radical-anion of glyoxal. The 532 nm photoelectron spectrum provides the first direct spectroscopic determination of the adiabatic electron affinity of glyoxal, EA = 1.10 ± 0.02 eV. This assignment is supported by a Franck-Condon simulation of the experimental spectrum that successfully reproduces the observed spectral features. The vertical detachment energy of the radical-anion is determined as VDE = 1.30 ± 0.04 eV. The reported EA and VDE values are attributed to the most stable (C 2h symmetry) isomers of the neutral and the anion.

Electron affinity and excited states of methylglyoxal

“…In Figure 1(a), a single photodetachment band labeled A is observed in each of the MG and G spectra. This congested transition is characterized by a predominantly perpendicular photoelectron anisotropy, as seen in the MG images in Figures 1(a) and 1(b) and reported previously for G. 1 Similar to G, feature A in all MG spectra in Figure 1 is assigned to the transition Abel-inverted (right) data, and the corresponding photoelectron spectrum. Band A in all spectra is assigned to the singlet ground state of the neutral molecule.…”

“…The 612 nm MG spectrum in (a) is presented in comparison with the previously reported 532 nm anion photoelectron spectrum of unsubstituted glyoxal (G). 1 For the ease of comparison, all spectra are plotted on the electron binding energy (eBE) scale, defined as eBE = hν eKE, where hν is the photon energy and eKE is electron kinetic energy.…”

“…17,18 The methylglyoxal solution (40% by weight in water) was first partially dehydrated using 3 Å molecular sieves with a 1:1 volume ratio for at least 24 h, until the solution turned yellowish. Unlike our previous experience with glyoxal, 1,19,20 the methylglyoxal solution did not require any methanol solvent to be extracted from the sieve mixture-it was simply decanted.…”

“…This work investigates the properties of methylglyoxal (MG) in comparison to its unsubstituted precursor-glyoxal (G), OHCCHO. 1 Although both G and MG are but minor components of Earth's atmosphere, their significant contributions to the chemistry of volatile organic compounds make them important players in the environment. [2][3][4][5][6][7][8][9][10][11][12] Despite their relative importance and rather elementary structures, some of the most fundamental properties of the G and MG molecules and their anions have remained unknown or poorly defined.…”

“…Only recently, the adiabatic electron affinity (EA) of glyoxal was determined directly using anion photoelectron spectroscopy: EA(G) = 1.10(2) eV. 1 This result is recommended to replace the only previous experimental (but indirect) estimate 12 of 0.62 (26) eV, still cited in most chemistry databases. 13 For methylglyoxal, no attempts to measure its electron affinity have been reported to date.…”