High Resolution Photoelectron Spectroscopy of the Acetyl Anion

Abstract

High-resolution photoelectron spectra of cryogenically cooled acetyl anions (CH 3 CO − ) 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 (ν 6 ), 834 ± 2 cm −1 (ν 7 ), and 471 ± 1 cm −1 (ν 8 ). This work represents the first experimental measurement of the ν 6 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.

High-Resolution Photoelectron Spectroscopy of Vibrationally Excited Vinoxide Anions

“…Images are acquired at a repetition rate of 20 Hz with a chargecoupled device (CCD) camera (768 × 768 pixels). Individual electron spots are event-counted and binned onto a 1024 × 1024 grid using the hybrid gradient-center of mass (HGCM) centroiding algorithm introduced in ref 60.…”

Spectroscopy of Radicals, Clusters, and Transition States Using Slow Electron Velocity-Map Imaging of Cryogenically Cooled Anions

“…The electron spots are event-counted, centroided, and binned into a 1024 × 1024 pixel grid. We have recently implemented new additions to the event-counting and centroiding algorithm that enable centroid analysis of overlapping electron spots, thereby improving the rate of data collection . Photoelectron centroids are accumulated over several thousand experimental cycles into a single velocity-mapped image, and the radial and angular distributions of the images are calculated using the Maximum Entropy Velocity Legendre Reconstruction (MEVELER) method or the more recently developed MELEXIR (Legendre Expanded Image Reconstruction) method .…”

“…We have recently implemented new additions to the event-counting and centroiding algorithm that enable centroid analysis of overlapping electron spots, thereby improving the rate of data collection. 54 Photoelectron centroids are accumulated over several thousand experimental cycles into a single velocity-mapped image, and the radial and angular distributions of the images are calculated using the Maximum Entropy Velocity Legendre Reconstruction (MEVELER) method 55 or the more recently developed MELEXIR (Legendre Expanded Image Reconstruction) method. 56 The electron kinetic energy (eKE) distributions are related to the radial distributions by acquiring images of the well characterized photodetachment transitions of various atomic anions such as O − at several different photon energies.…”

High-Resolution Photoelectron Spectroscopy of Vibrationally Excited Vinoxide Anions

“…Individual electron spots are event-counted and binned onto a 1024×1024 grid using the hybrid gradient-center of mass (HGCM) centroiding algorithm introduced in Ref. 58.…”