Electron affinity and excited states of methylglyoxal

• Main Authors: Dauletyarov, Yerbolat, Dixon, Andrew R., Wallace, Adam A., Sanov, Andrei
• Other Authors: Univ Arizona, Dept Chem & Biochem
• Language: en
• Published: AMER INST PHYSICS 2017
• Online Access: http://hdl.handle.net/10150/624155; http://arizona.openrepository.com/arizona/handle/10150/624155

Using photoelectron imaging spectroscopy, we characterized the anion of methylglyoxal (X(2)A" electronic state) and three lowest electronic states of the neutral methylglyoxal molecule: the closed-shell singlet ground state (X(1)A'), the lowest triplet state (a(3)A"), and the open-shell singlet state (A(1)A"). The adiabatic electron affinity (EA) of the ground state, EA(X(1)A') = 0.87(1) eV, spectroscopically determined for the first time, compares to 1.10(2) eV for unsubstituted glyoxal. The EAs (adiabatic attachment energies) of two excited states of methylglyoxal were also determined: EA(a(3)A") = 3.27(2) eV and EA(A(1)A") = 3.614(9) eV. The photodetachment of the anion to each of these two states produces the neutral species near the respective structural equilibria; hence, the a(3)A" <- X(2)A" and A(1)A" <- X(2)A" photodetachment transitions are dominated by intense peaks at their respective origins. The lowest-energy photodetachment transition, on the other hand, involves significant geometry relaxation in the X(1)A' state, which corresponds to a 60 degrees internal rotation of the methyl group, compared to the anion structure. Accordingly, the X(1)A' <- X(2)A" transition is characterized as a broad, congested band, whose vertical detachment energy, VDE = 1.20(4) eV, significantly exceeds the adiabatic EA. The experimental results are in excellent agreement with the ab initio predictions using several equation-of-motion methodologies, combined with coupled-cluster theory. Published by AIP Publishing.