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

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.