Rovibronic structure in slow photoelectron velocity-map imaging spectroscopy of CH2CN⁻ and CD2CN⁻

Marissa L Weichman; Jongjin B Kim; Daniel M Neumark

doi:10.1063/1.4867501

Rovibronic structure in slow photoelectron velocity-map imaging spectroscopy of CH2CN⁻ and CD2CN⁻

J Chem Phys. 2014 Mar 14;140(10):104305. doi: 10.1063/1.4867501.

Authors

Marissa L Weichman¹, Jongjin B Kim¹, Daniel M Neumark¹

Affiliation

¹ Department of Chemistry, University of California, Berkeley, California 94720, USA.

PMID: 24628167
DOI: 10.1063/1.4867501

Abstract

We report high-resolution anion photoelectron spectra of the cryogenically cooled cyanomethide anion, CH2CN(-), and its isotopologue, CD2CN(-), using slow photoelectron velocity-map imaging (SEVI) spectroscopy. Electron affinities of 12 468(2) cm(-1) for CH2CN and 12 402(2) cm(-1) for CD2CN are obtained, demonstrating greater precision than previous experiments. New vibrational structure is resolved for both neutral species, especially activity of the ν5 hydrogen umbrella modes. The ν6 out-of-plane bending mode fundamental frequency is measured for the first time in both systems and found to be 420(10) cm(-1) for CH2CN and 389(8) cm(-1) for CD2CN. Some rotational structure is resolved, allowing for accurate extraction of vibrational frequencies. Temperature-dependent SEVI spectra show marked effects ascribed to controlled population of low-lying anion vibrational levels. We directly measure the inversion splitting between the first two vibrational levels of the anion ν5 umbrella mode in both species, finding a splitting of 130(20) cm(-1) for CH2CN(-) and 81(20) cm(-1) for CD2CN(-). Franck-Condon forbidden activity is observed and attributed to mode-specific vibrational autodetachment from the CH2CN(-) and CD2CN(-) dipole bound excited states. We also refine the binding energy of the anion dipole bound states to 39 and 42 cm(-1), respectively, for CH2CN(-) and CD2CN(-).