Vibronic Structure of the Formyloxyl Radical (HCO₂) via Slow Photoelectron Velocity-Map Imaging Spectroscopy and Model Hamiltonian Calculations

Abstract

We report high-resolution photoelectron spectra of HCO 2 -and DCO 2 -obtained with slow photoelectron velocity-map imaging. Well-resolved photodetachment transitions to the 2 A 1 and 2 B 2 states of the neutral radicals were observed. In addition, vibronic levels of the HCO 2 and DCO 2 radicals with up to 2000 cm -1 of internal energy were calculated using a quasidiabatic Hamiltonian approach and high-level ab initio calculations. Spectral simulations using the calculated levels were found to be in excellent agreement with the experimental spectra and used to assign many of its features. This study unambiguously determined that the 2 A 1 state is the ground state of both HCO 2 and DCO 2 , in contrast to earlier work that indicated the 2 B 2 state was the ground state for DCO 2 . For both isotopologs, the 2 B 2 state is a very low-lying excited state with term energies of T 0 ) 318 ( 8 cm -1 for HCO 2 and T 0 ) 87 ( 8 cm -1 for DCO 2 . The adiabatic electron affinities are determined to be EA(HCO 2 ) ) 3.4961 ( 0.0010 eV and EA(DCO 2 ) ) 3.5164 ( 0.0010 eV.

Communication: Observation of dipole-bound state and high-resolution photoelectron imaging of cold acetate anions

“…7 The s-wave PAD of the 0 0 0 peak indicates that the highest occupied molecular orbital of CH 3 COO − should be a p-type orbital, which is quite different from what was observed for HCOO − : the PAD of the 0 0 0 peak of HCOO• has p-wave character. 21 Moreover, the observed p-wave PAD of the excited state of CH 3 COO − is also different from that reported for the first excited electronic state of HCOO•. Our observed PAD of the PE images of CH 3 COO − is consistent with the theoretical predication that the ground state of CH 3 COO• is 2 A ′′ (B 2 ) with the 2 A ′ (A ′ ) low-lying excited state.…”

“…21 Photoelectrons corresponding to the ground state ( 2 A 1 ) of HCOO• have p-wave character and those corresponding to the 2 B 2 excited state, which lies only 218 ± 121 cm −1 higher, have s-wave character. 21 While information about photoelectron angular distribution (PAD) of CH 3 COO• is lacking, ab inito calculations indicated that the symmetry of the ground state of CH 3 COO• is different from that for HCOO•, that is, the ground state of CH 3 COO• is 2 A ′′ (B 2 ), with a 2 A ′ (A ′ ) lowlying excited state ∼0.1-0.2 eV higher in energy. 7 Molecules with sufficient dipole moments can bind an electron [22][23][24][25] and form dipole-bound anions.…”

“…20 The vibronic structure of HCOO• has been reported via slow electron velocity-map imaging (SEVI) spectroscopy, giving rise to an accurate EA of 3.4961 ± 0.0010 eV. 21 Photoelectrons corresponding to the ground state ( 2 A 1 ) of HCOO• have p-wave character and those corresponding to the 2 B 2 excited state, which lies only 218 ± 121 cm −1 higher, have s-wave character. 21 While information about photoelectron angular distribution (PAD) of CH 3 COO• is lacking, ab inito calculations indicated that the symmetry of the ground state of CH 3 COO• is different from that for HCOO•, that is, the ground state of CH 3 COO• is 2 A ′′ (B 2 ), with a 2 A ′ (A ′ ) lowlying excited state ∼0.1-0.2 eV higher in energy.…”

Ground and low-lying excited states of propadienylidene (H2C=C=C:) obtained by negative ion photoelectron spectroscopy

“…All of the summations are restricted in the sense that each contribution is nonvanishing only if it contains a totally symmetric product of normal coordinates. Consistent with our earlier work on the formyloxyl radical 53 -as well as a recent study of the electronic absorption spectrum of H 2 CCC (Ref. 19)-the cubic and quartic force constants above are limited to those which contain only totally symmetric coordinates q 1 through q 4 .…”

“…The procedure for Hamiltonian parametrization used here is essentially identical to that used in two previous studies in which both good quantitative (∼50 cm −1 or better in level positions) and qualitative agreement was achieved between experimental and theoretical spectra. 53,56 Once constructed, the model Hamiltonian was diagonalized using Lanczos recursions. 63 The spectra shown here included thirty basis functions for modes q 2 , q 3 , and q 4 in all cases.…”