The methoxy free radical has been formed in a supersonic free jet expansion by KrF photolysis of methyl nitrite. Its laser-induced fluorescence excitation and wavelength-resolved emission spectra have been recorded at low temperature. This paper reports the vibronic analysis of the CH30 and CD30 A^* * X2E electronic spectra. A new value for the electronic origin has been determined as well as a nearly complete set of vibrational frequencies.

Five bands of the B̃–X̃ laser induced fluorescence spectrum of jet-cooled 1-propoxy radical have been recorded with a spectral resolution of ≈200 MHz. The resolved rotational and fine structure of these bands has been assigned and analyzed providing rotational constants for both the X̃ and B̃ states as well as components of the electron spin-rotation tensor in the X̃ state. By comparison of these constants with ones obtained from quantum chemistry calculations, two bands have been assigned to the gauche (G) conformer of 1-propoxy and 3 bands to the trans (T) conformer. The spectrum of each conformer abruptly terminates after the excitation of a single C–O stretch.

The laser-induced fluorescence spectra of jet-cooled alkoxy radicals were recorded. Spectra were observed for both isomers of propoxy and all three isomers of butoxy. In nearly all cases, the vibrational structure of the spectra are dominated by a C-O stretch progression, which, however, terminates much more abruptly for the primary isomers than for the more branched ones. For each of the radicals (except t-butoxy), a number of low-frequency (below the C-O stretch) vibrational modes were assigned by analogies among the alkoxy spectra and reference to frequencies from ab initio calculations. A few higher frequency modes were also assigned using similar approaches.

Laser induced fluorescence spectra of nearly 20 jet-cooled alkoxy free radicals, with up to 12 carbon atoms, have been observed. Trends, as a function of the number of carbon atoms, are reported for origin frequencies, and their dependence upon structural isomers are documented. The interpretation of various bands in the spectra, and their rotational contours, in terms of excited-state vibrations and/or different conformations is discussed.

High resolution electronic spectroscopy and an empirical potential energy surface for NeSH/D J. Chem. Phys. 110, 5065 (1999); 10.1063/1.478395High resolution electronic spectroscopy of KrOH/D and an empirical potential energy surface Experimental data from vibrationally and rotationally resolved laser induced fluorescence experiments have been used to produce potential energy surfaces ͑PES͒ for the excited à 2 ⌺ ϩ states of the Ar•SH and Kr•SH van der Waals complexes. This was done using a potential energy functional form first suggested by Bowman and co-workers ͓J. Phys. Chem. 94, 2226, 8858 ͑1990͒; Chem. Phys. Lett. 189, 487 ͑1992͔͒ for Ar•OH/D. A discrete variable representation ͑DVR͒ of the vibration-rotation Hamiltonian was used in combination with the implicitly restarted Lanczos method and sequential diagonalization truncation ͑SDT͒ of the DVR Hamiltonian. This approach takes advantage of the sparseness of the DVR Hamiltonian and the reduced order of the SDT representation. This combination of methods greatly reduces the amount of computational time needed to determine the eigenvalues of interest. This is important for the determination of the PES that results from minimizing the difference between the experimental and theoretically predicted values for the vibronic energy levels and their corresponding rotational constants. In addition this procedure was helpful in assigning the absolute vibrational quantum numbers for the deuterated species for which less experimental data was available. Plots of the calculated wavefunctions corresponding to various experimentally vibronic bands indicate that these states sample regions of the PES from 0 degrees, where the hydrogen atom is closest to the rare gas atom, to approximately the saddle point, near the T-shaped configuration. As a result this region of the surface is determined accurately whereas the region of the PES around 180 degrees, corresponding to the sulfur atom being closest to the rare gas atom, is determined only qualitatively.