Channel branching ratios in CH2CN− photodetachment: Rotational structure and vibrational energy redistribution in autodetachment

Abstract

We report photoelectron spectra of CHCN, recorded at photon energies between 13 460 and 15 384 cm, which show rapid intensity variations in particular detachment channels. The branching ratios for various spectral features reveal rotational structure associated with autodetachment from an intermediate anion state. Calculations using equation-of-motion coupled-cluster method with single and double excitations reveal the presence of two dipole-bound excited anion states (a singlet and a triplet). The computed oscillator strength for the transition to the singlet dipole-bound state provides an estimate of the autodetachment channel contribution to the total photoelectron yield. Analysis of the different spectral features allows identification of the dipole-bound and neutral vibrational levels involved in the autodetachment processes. For the most part, the autodetachment channels are consistent with the vibrational propensity rule and normal mode expectation. However, examination of the rotational structure shows that autodetachment from the ν (v = 1 and v = 2) levels of the dipole-bound state displays behavior counter to the normal mode expectation with the final state vibrational level belonging to a different mode.

Emerging Nonvalence Anion States of [Isoprene-H·]·H2O Accessed via Detachment of OH–·Isoprene

“…In this case, low-frequency modes of the transition state complex are encoded in the e – KE’s of the autodetached electrons. Assuming the Δv = −1 propensity rule for vibrational autodetachment, − the e – KE values encode the vibrational spacings of various modes in the DBS, which in general are nearly identical to those of the neutral, minus the binding energy of the DBS. The initially planar butadiene backbone is slightly buckled in the neutral [Isoprene-H • ] radical, suggesting the vibrational modes involve the low-frequency backbone bend modes.…”

Velocity Map Imaging Spectroscopy of the Dipole-Bound State of CH2CN–: Implications for the Diffuse Interstellar Bands

“…In this work, the DBS chemistry of CH 2 CN – is explored by using a high-resolution photoelectron imaging (HR-PEI) spectrometer. CH 2 CN – is one of the most studied DBS systems and has been shown to undergo both vibrational , and rotational − autodetachment. Furthermore, rotational constants of both the anion and DBS have been accurately determined in a seminal very high-resolution (20 MHz) photodetachment cross-section study .…”

Observation of a Symmetry-Forbidden Excited Quadrupole-Bound State

“…Stable valence-bound anions with polar neutral cores can support dipole-bound excited states just below the electron detachment threshold. − DBSs as a special class of electronically excited states of valence-bound anions have allowed the observations of vibrational mode-specific autodetachment and the realization of resonant photoelectron spectroscopy (rPES), − which yields much richer spectroscopic information than conventional anion PES for relatively complicated molecular systems. Dipole-bound states in simpler molecular anions including diatomic species have been observed recently. − The autodetachment lifetimes from different vibrational levels of the excited DBS of the phenoxide anion have been directly measured using a pump–probe technique in a very recent study …”