Xinming Zhu

Laser excitation and emission spectroscopy of the methoxy radical in a supersonic jet

Abstract Laser-induced excitation and wavelength-resolved emission spectra of the methoxy (CH 3 O) radical have been obtained in a supersonic jet environment. Fluorescence in the near ultraviolet from several vibronic bands belonging to the A 2 A 1 - X 2 E electronic system of CH 3 O has been dispersed by a 0.6 m monochromator with a resolution of 0.3 nm. A complete set of vibrational frequencies with all assignments for the X 2 E state of CH 3 O has been obtained. To the best of our knowledge, the dispersed spectra of CH 3 O for the 2 2 0 and 2 1 0 3 1 0 bands are presented here for the first time. The vibrational constants determined by a least-squares fit for the ν 3 mode are ω″ e = 1071 cm −1 and ω″ e x ″ e = 8.4 cm −1 . For the Jahn-Teller active ν 6 mode, the vibrational and anharmonic constants ω″ e = 786 cm −1 and ω″ e x ″ e = 55 cm −1 , respectively, have been obtained for the first time.

Laser optogalvanic wavelength calibration with a commercial hollow cathode iron-neon discharge lamp

Abstract-351 optogalvanic transitions have been observed in the 337-598 nm wavelength region using an iron-neon hollow cathode discharge lamp and a pulsed tunable dye laser. 223 of these have been identified as transitions associated with neon energy levels. These optogalvanic transitions have allowed, in conjunction with interference fringes recorded concomitantly with an etalon, the calibration of the dye laser wavelength with 0.3 cm-’ accuracy. INTRODUCTION Wavelength calibration of tunable lasers is important in experimental laser spectroscopy. An iodine absorption cell can be used for precise calibration of the spectral region 50&675 nm in the visible, since a good atlas exists for that region. ’ However, in the blue and near U.V. regions of the electromagnetic spectrum, there is a paucity of suitable species for wavelength calibration of tunable lasers. Tellurium has been employed by Miller.’ However, its spectral atlas is not easily accessible. The optogalvanic (OG) effect provides a good solution for wavelength calibration inadequacies in the visible and near U.V. regions of the electromagnetic spectrum. The OG effect, discovered by Penning3 in 1928, is the impedance change of a neon discharge tube when illuminated by a second neon discharge tube. In 1976, Green et al4 observed the OG effect with a tunable dye laser and measured the changes in voltage across a low-pressure gas discharge tube irradiated by a laser beam that was tuned to the wavelength of transition of a species present in the discharge. These authors reported optogalvanic signals for transitions involving lithium, sodium, calcium, barium, uranium, neon, and helium. It was pointed out4 that the OG effect might have significant impact in optical spectroscopy and other areas of applied physics and chemistry. Extensive work has since been carried out to understand the OG effect in some detail and to use it in laser spectroscopy. Precise wavelength calibration of tunable lasers is an important application of the OG effect. OG lines have been observed in case of various species sputtered from hollow cathodesk9 and from fill gases such as neon and argon. 4~‘S’9 A larger discharge current (> 20 mA) is needed for exciting OG transitions associated with species sputtered from cathodes as compared to the signal from the gas atoms. Uranium, for example, is a good candidate for producing the OG effect, because it is an excellent wavelength standard. In addition, uranium gives rise to spectral lines that are narrow and do not possess hyperfine structure over a wide spectral region extending from the infrared to the ultraviolet. However, the OG signals arising from discharge gases are usually much stronger than those from cathode elements. OG transitions from argon have been observed in the wavelength regions 367422 nm,19 415-670 nm,” 425-700 nrn,j4 420-740 nm,16 555-575 nm,” 727-772 nm,13 360-740 nm,‘* 244&2780 nm.” OG signals with commercial neon lamps, which are

Laser-induced excitation and dispersed fluorescence spectra of the ethoxy radical

Extensive laser excitation and dispersed fluorescence spectra of the ethoxy radical have been recorded in a supersonic jet expansion. Neon transitions have been used to calibrate both the wavelength of the excitation dye laser and the optical multichannel analyser system used to record the wavelength-resolved emission spectra. Both the excitation and dispersed spectra are characterized by prominent progressions involving the C - O stretch vibrational mode. Seven vibrational frequencies for the excited electronic state and eight for the ground state have been assigned. To the best of our knowledge, 10 of these 15 assigned frequencies are reported here for the first time. Vibrational and anharmonic constants for the C - O stretch mode have been determined via least-squares fits for the X state and the B state .

Rotationally-resolved excitation spectroscopy of the methoxy radical in a supersonic jet

Abstract Laser-induced fluorescence excitation spectra of the methoxy radical have been obtained under sufficiently high resolution in a supersonic jet expansion. The rotational structure associated with its origin band has been identified in the midst of strong overlapping rotational transitions due to the hydroxyl radical in the 31490–31700 cm−1 spectral region. Rotationally-resolved A 2A1 - X 2E spectra of the 00 0 band of methoxy have been explicitly assigned using the nomenclature for prolate symmetric top transitions in doublet states.

Polarity of Laser Excited Optogalvanic Transitions in Neon

Abstract Irradiation of a gaseous discharge with a tunable laser produces observable voltage changes at wavelengths that correspond to electronic transitions for species within the discharge. Optogalvanic (OG) transitions of neon have been investigated in the visible and near UV regions by axially irradiating a hollow cathode discharge with an excimer-pumped dye laser. A variety of OG transitions that originate from metastable states have been recorded. A digital oscilloscope was used to record the waveforms of the OG transitions. The polarities of 29 OG transitions recorded in the near UV and visible are explained in terms of processes that affect the population of neon atoms in metastable states.