Multiphoton ionization spectra of radical products in the F(2P)+ketene system: Spectral assignments and formation reaction for CH2F, observation of CF and CH

Abstract

The reactions of F(2P)+ketene and F(2P)+ketene-d2 were studied in a flow reactor. Spectra of the radical products CH2F, CD2F, CH, CF, and atomic carbon were detected between 292–395 nm by resonance enhanced multiphoton ionization (REMPI) mass spectrometry. Fluoromethyl radicals were identified as a major product of the F+ketene elementary reaction. REMPI spectra of fluoromethyl radicals originated from two-photon preparation of 3p, 4p, and 5p Rydberg states (quantum defect ∼0.6). Absorption of a third laser photon ionized the radicals, a 2+1 REMPI mechanism. Rydberg band origins were observed in CH2F at ν00=52 863, 63 275, and 67 265 cm−1 and in CD2F at ν00=52 786, 63 195, and 67 186 cm−1. A normal mode analysis revealed the vibrational frequencies of the C–F stretch, CH2 scissors, and out-of-plane bending modes in the Rydberg states. The ground state out-of-plane bending frequency in CH2F is 260(30) cm−1 and in CD2F it is 170(30) cm−1. CH radicals were generated by the photolysis of ketene and observed at ∼311 nm by two-photon excitation through the D 2Π(v′=2) ←←X 2Πr band. The reaction mechanism that generated the CF radicals was not determined. The REMPI CF radical spectrum generated by a 2+1 photon mechanism appeared as a series of bandheads described by the constants ν00=∼52 572 cm−1, ωe =1820 cm−1, and ωexe =−18.2 cm−1.