High Resolution Photoelectron Spectroscopy of the Acetyl Anion

Martin DeWitt; Mark C Babin; Jascha A Lau; Tonia Solomis; Daniel M Neumark

doi:10.1021/acs.jpca.2c06214

High Resolution Photoelectron Spectroscopy of the Acetyl Anion

J Phys Chem A. 2022 Nov 3;126(43):7962-7970. doi: 10.1021/acs.jpca.2c06214. Epub 2022 Oct 21.

Authors

Martin DeWitt¹, Mark C Babin¹, Jascha A Lau¹, Tonia Solomis¹, Daniel M Neumark^{1

2}

Affiliations

¹ Department of Chemistry, University of California, Berkeley, California94720, United States.
² Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States.

PMID: 36269316
DOI: 10.1021/acs.jpca.2c06214

Abstract

High-resolution photoelectron spectra of cryogenically cooled acetyl anions (CH₃CO^-) obtained using slow photoelectron velocity-map imaging are reported. The high resolution of the photoelectron spectrum yields a refined electron affinity of 0.4352 ± 0.0012 eV for the acetyl radical as well as the observation of a new vibronic structure that is assigned based on ab initio calculations. Three vibrational frequencies of the neutral radical are measured to be 1047 ± 3 cm^-1 (ν₆), 834 ± 2 cm^-1 (ν₇), and 471 ± 1 cm^-1 (ν₈). This work represents the first experimental measurement of the ν₆ frequency of the neutral. The measured electron affinity is used to calculate a refined value of 1641.35 ± 0.42 kJ mol^-1 for the gas-phase acidity of acetaldehyde. Analysis of the photoelectron angular distributions provides insight into the character of the highest occupied molecular orbital of the anion, revealing a molecular orbital with strong d-character. Additionally, details of a new centroiding algorithm based on finite differences, which has the potential to decrease data acquisition times by an order of magnitude at no cost to accuracy, are provided.