Structural characterization of electron-induced proton transfer in the formic acid dimer anion, (HCOOH) <inf>2</inf>^-, with vibrational and photoelectron spectroscopies

The (HCOOH) 2 anion, formed by electron attachment to the formic acid dimer (FA 2), is an archetypal system for exploring the mechanics of the electron-induced proton transfer motif that is purported to occur when neutral nucleic acid base-pairs accommodate an excess electron K. Aflatooni, G. A. Gallup, and P. D. Burrow, J. Phys. Chem. A 102, 6205 (1998)10.1021/jp980865n; J. H. Hendricks, S. A. Lyapustina, H. L. de Clercq, J. T. Snodgrass, and K. H. Bowen, J. Chem Phys. 104, 7788 (1996)10.1063/1.471484; C. Desfrancois, H. Abdoul-Carime, and J. P. Schermann, J. Chem Phys. 104, 7792 (1996). The FA 2 anion and several of its HD isotopologues were isolated in the gas phase and characterized using Ar-tagged vibrational predissociation and electron autodetachment spectroscopies. The photoelectron spectrum of the FA 2 anion was also recorded using velocity-map imaging. The resulting spectroscopic information verifies the equilibrium FA 2- geometry predicted by theory which features a symmetrical, double H-bonded bridge effectively linking together constituents that most closely resemble the formate ion and a dihydroxymethyl radical. The spectroscopic signatures of this ion were analyzed with the aid of calculated anharmonic vibrational band patterns. © 2012 American Institute of Physics