Two-photon resonant ionization spectroscopy of the allyl-h5 and allyl-d5 radicals:  Rydberg states and ionization energies

Abstract

The vibronic spectra of allyl-h5 (CH2CHCH2) and allyl-d5 (CD2CDCD2) radicals at 6.0–8.2 eV have been observed using 2+1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The allyl-h5 and allyl-d5 radicals were produced in the nozzle of a supersonic jet expansion by the pyrolysis of CH2CHCH2I and CD2CDCD2Br, respectively. Together with our previous study, Rydberg states of ns (n=4–12) for allyl-h5 and (n=4–10) for allyl-d5 have been observed in the REMPI spectra. Prominent vibrational progressions with the spacings of ∼440 cm−1 in allyl-h5 and ∼360 cm−1 in allyl-d5 are observed in the s Rydberg series. The totally symmetric ∠CCC-bending mode is responsible for the vibrational progressions. Facilitated with ab initio calculated Franck–Condon factors, other vibrations (CH2 rocking and C3 stretching) observed in the s Rydberg series have also been identified. The adiabatic ionization energies, 65 594±9 cm−1 (8.133±0.001 eV) for allyl-h5 and 65 527±16 cm−1 (8.124±0.002 eV) for allyl-d5, are extrapolated from the convergence of the observed ns Rydberg series.

Single-photon and resonance-enhanced multiphoton threshold ionization of the allyl radical

“…Slightly higher values, ranging up to 8.15 eV, were reported in later works. [13][14][15][16] The most recent measurements of the adiabatic ionization energy of allyl carried out by pulsed-fieldionization zero-kinetic-energy ͑PFI-ZEKE͒ photoelectron spectroscopy using multiphoton 14 and single-photon excitation schemes 17,18 yielded values differing by as much as 22 meV. These measurements provided important information on the vibrational energy level structure of C 3 H 5 + .…”

Exploring the Excited-State Dynamics of Hydrocarbon Radicals, Biradicals, and Carbenes Using Time-Resolved Photoelectron Spectroscopy and Field-Induced Surface Hopping Simulations

“…The allyl radical is one of the simplest resonance-stabilized hydrocarbons and an important model for the spectroscopy and dynamics of radicals . It is therefore not surprising that it has aroused considerable interest over the years, which resulted in numerous experimental investigations, employing methods such as ESR, IR, Raman, − rotational and rovibrational spectroscopy, , electron diffraction, multiphoton ionization (MPI), ,− and photoelectron spectroscopy. − In parallel, a multitude of theoretical studies has also been performed, covering fundamental aspects such as electron delocalization, spin density distribution, or wave function stability as well as investigating the vibrational spectra, − excited electronic states, − and photochemical reactions . Here we will focus on the influence of a methyl group on the excited-state dynamics by comparing the allyl radical with its 1- and 2‑methylated counterparts (1MA & 2MA).…”