Journal of Physical Chemistry A, Vol.118, No.10, 1826-1831, 2014
Resonance-Enhanced Multiphoton Ionization of CH2Br2: Rydberg States, Photofragmentation, and CH Spectra
Mass-resolved (2 + n) resonance-enhanced multiphoton ionization (REMPI) spectra of CH2Br2 in the two-photon resonance excitation region from 71 200 to 82 300 cm(-1) were recorded and analyzed. Spectral structures allowed characterization of new molecular Rydberg states. C*(D-1(2)) was found to be an important intermediate in the photodissociation processes. A broad spectral feature peaking at about 80 663 cm(-1) in the C+ spectrum and frequently seen in related studies is reinterpreted and associated with switching between three- and two-photon ionization of C*(D-1(2)). Analysis of band structures due to transitions from the A(2)Delta state of CH* that were seen in the CH+ and C+ REMPI spectra allowed characterization of three electronic states of CH, assigned as E-2 Pi, D-2 Pi, and F-2 Sigma(+), which clarifies a long-term puzzle concerning the energetics of the CH radical. Predissociation of the E, D, and F states to form C*(D-1(2)) occurs. Bromine atomic lines were observed and are believed to be associated with bromine atom formation via predissociation of CH2Br2 Rydberg states.