Two photon resonance enhanced multiphoton ionization spectroscopy and state assignments of the methyl radical

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Abstract
A mass resolved multiphoton ionization spectroscopy study of CH3 and CD3 has revealed two new electronic Rydberg series in these radicals. Simultaneous absorption of two photons prepared the excited states. Absorption of a third photon from the excited state generated the parent ions of methyl radical (m/z 15; CH3 and m/z 18; CD3) which were detected in a quadrupole mass spectrometer. The np 2A″2 Rydberg series was detected and identified by a rotational assignment of the 3p 2A″2 state of CD3 and by a polarization study of the np states. The quantum defect of this series was 0.6. The rotational constants determined for the ground and 3p 2A″2 excited states were B″0=4.798 cm−1 and B′0=4.768 cm−1. A vibrational analysis shows that both the symmetric stretch and out‐of‐plane bending mode are active in the 3p 2A″2 state. A second Rydberg series with a quantum defect of zero was detected and tentitively assigned to the nf 2E′ series.