David E. Powers

Rovibronic analysis of the laser induced fluorescence excitation spectrum of the jet-cooled methoxy radical

The laser induced fluoresence excitation spectrum for the A 2A1↔X 2E transition of the methoxy radical has been reinvestigated. An extensive set of vibrational levels has been assigned with the aid of increased vibrational and rotational cooling. Many of these vibrational assignments are confirmed by rotational analysis of bands involving both the symmetric and asymmetric fundamentals of the A state as well as vibrations containing two quanta of the e modes. Although parts of the vibrational structure have been assigned previously, several discrepancies are identified and corrected. Vibrational frequencies have been obtained for all the modes in the A 2A1 state of the molecule. The Fermi resonance that exists between ν3 and ν2 has been investigated and interaction constants describing it have been obtained.

Vibrational mode and frequency dependence of the photofragmentation of the methoxy radical

The photodissociation process for the jet-cooled methoxy radical at energies above the origin of the A state has been probed by several techniques: laser induced fluorescence, fluorescence temporal decay, and fluorescence depletion spectroscopy. A threshold for this process is clearly established. Above that threshold the ratio for the competing processes of photon emission and bond fission vary strongly. This variation is a function not only of the total excitation energy but is also strongly mediated by the nature of the vibrational motion involved. It is found that excitation of the ν3 mode (or other components in Fermi resonance with it) strongly promotes the breaking of the C–O bond.

The spectroscopy of the CdCH3 radical and its positive ion

Resonantly enhanced multiphoton ionization, REMPI (2 color, 1+1′), and zero electron kinetic energy-pulsed field ionization, ZEKE-PFI, spectra are reported for the first organometallic radical, CdCH3. The combined REMPI and ZEKE-PFI data have necessitated a change of assignment for one of the bands of the A2E←X 2A1 electronic transition of the neutral radical. The new assignment and the revised molecular parameters are reported. The ZEKE-PFI spectrum yields the adiabatic ionization potential for the CdCH3 radical and four of the six possible vibrational frequencies of its cation. Clearly resolved rotational (K level) structure is observed in some bands of the ZEKE-PFI spectrum, providing a unique experimental test for newly extended ZEKE-PFI rotational selection rules.

Laser-induced fluorescence and fluorescence depletion spectroscopy of the jet-cooled CF3S radical

Abstract The spectrum of the CF 3 S free radical has been observed for the first time cooled in a supersonic free jet expansion. Both ‘bright’ and ‘dark’ levels of the A state have been observed using a combination of laser-induced fluorescence and fluorescence depletion spectroscopy. The photofragmentation of CF 3 S is shown to be very mode specific.