The A˜(2)E(″)←X˜(2)A2 (') spectrum of NO3 radical from 7550 cm(-1) to 9750 cm(-1) has been recorded and analyzed. Our spectrum differs from previously recorded spectra of this transition due to jet-cooling, which narrows the rotational contours and eliminates spectral interference from hot bands. Assignments of numerous vibronic features can be made based on both band contour and position including the previously unassigned 30 (1) band and several associated combination bands. We have analyzed our spectrum first with an independent anharmonic oscillator model and then by a quadratic Jahn-Teller vibronic coupling model. The fit achieved with the quadratic Jahn-Teller model is excellent, but the potential energy surface obtained with the fitted parameters is in only qualitative agreement with one obtained from ab initio calculations.

The jet-cooled Ã-X̃ near IR origin band spectra of the G(1)G(2)G(3) conformer of four β-hydroxyethylperoxy isotopologues, β-HEP (HOCH(2)CH(2)OO), β-DHEP (DOCH(2)CH(2)OO), β-HEP-d(4) (HOCD(2)CD(2)OO), and β-DHEP-d(4) (DOCD(2)CD(2)OO), have been recorded by a cavity ringdown spectrometer with a laser source linewidth of ~70 MHz. The spectra of all four isotopologues have been analyzed and successfully simulated with an evolutionary algorithm, confirming the cyclic structure of the molecule responsible for the observed origin band. The analysis also provides experimental à and X̃ state rotational constants and the orientation of the transition dipole moment in the inertial axis system; these quantities are compared to results from electronic structure calculations. The observed, broad linewidth (Δν > 2 GHz) is attributed to a shortened lifetime of the à state associated with dynamics along the reaction path for hydrogen transfer from the OH to OO group.

A moderate resolution spectrum of the A 2 E state of the NO 3 radical has been obtained using jet-cooled cavity ringdown spectroscopy. The analysis of the vibronic structure of this spectrum has been undertaken using a quadratic Jahn-Teller Hamiltonian. All observed transitions have been assigned and unperturbed frequencies and Jahn-Teller coupling constants were determined by fitting the experimental spectrum using nonlinear least squares regression. We find evidence of strong Jahn-Teller coupling in this electronic state, particularly in the ν 3 mode. These results are compared to electronic structure calculations including terms up to fourth order. Calculated and experimental spectra are presented and critically compared.

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