Laser-based spectroscopy of FeD: Excitations to the g 6Φ electronic state.

Bands of the g 6Φ-X 4Δ, g 6Φ-A 4Π, g 6Φ-a 6Δ, and g 6Φ-b 6Π electronic transitions of iron monodeuteride (FeD) have been measured in laser excitation and in dispersed fluorescence. The molecules were produced both in a cold supersonic molecular jet source and in a chemical reaction between iron pentacarbonyl [Fe(CO5)] and a microwave discharge of argon and hydrogen gases. Dispersed fluorescence from the latter source was detected at high resolution with a Fourier transform spectrometer, yielding a large number of the transitions observed. The data reveal that FeD experiences strong interstate couplings that compromise fitting of the data with traditional Hamiltonians but that the problem is less severe than in corresponding spectra of FeH. This work greatly expands the available data on FeD, which were previously characterized only through the F 4Δ-X 4Δ spectrum and pure rotational data in the ground state.

High-Resolution Far-Infrared Spectroscopy of N-Substituted Two-Ring Polycyclic Aromatic Hydrocarbons: An Extended Study.

Polycyclic aromatic hydrocarbons (PAHs) and their N-substituted derivatives are among the largest species for which gas-phase high-resolution spectroscopy can be performed nowadays. In this paper we report the observation and analysis of spectra from several N-substituted two-ring PAHs, all taken in the "fingerprint" far-infrared region (<850 cm(-1)). Together with accurate measurements of their pure rotational transitions in the millimeter and submillimeter ranges, these synchrotron-based Fourier transform infrared (FTIR) measurements provide an accurate description of the rotational energy levels in the ground and low-energy excited vibrational states of these species. To complement the experimental data, anharmonic DFT calculations were performed to obtain relatively accurate rotational and vibrational parameters. The calculated results strongly support the rotational analysis and provide a good estimate of the equilibrium structures for each species. Extended measurements, analysis, and calculations are presented here for the far-IR bands of quinoline (C9H7N), isoquinoline (C9H7N), quinoxaline (C8H6N2), quinazoline (C8H6N2), [1,5]-naphthyridine (C8H6N2), [1,6]-naphthyridine (C8H6N2), and indole (C8H7N) molecules.

Optogalvanic spectroscopy of the C"5Pi ui-A' 5Sigma+g electronic system of N2.

We have recorded spectra involving the 3-1, 4-2, 2-0, and 2-2 bands of the C" 5Pi(ui)-A' (5)Sigma+(g) electronic system of N(2) using optogalvanic detection in a discharge through a supersonic jet expansion of argon mixed with a trace of nitrogen gas. The spectra have an effective rotational temperature of about 45 K. They involve all five spin-orbit components of the C" 5Pi(ui) state, which has allowed for precise determination of the spin-orbit coupling in this state. Analysis of the C" 5Pi(ui) state Lambda-doubling shows that it is caused primarily by a first-order spin-spin effect rather than by interaction with Sigma(u) (+/-) states. Our results allow us to assign lines in the 4-2 and 2-0 bands observed in a fluorescence depletion experiment conducted over ten years ago [Ch. Ottinger and A. F. Vilesov, J. Chem. Phys. 103, 9929 (1995)], and to comment on the suggestion that perturbations to the C (3)Pi(u) v=1 level of N(2) arise from interactions with the C" 5Pi(ui) state.

Experimental determination of a spin-orbit interval in the C" 5Pi(ui) state of 14N2.

We have developed an experimental setup using the combination of laser optogalvanic detection and a supersonic expansion of excited N2 to record the high resolution spectrum of the (3-1) and (4-2) Herman infrared bands (C" 5Pi(ui)-A' 5Sigma(g)+). We report the first experimental determination of a spin-orbit interval (about 24 cm(-1)) in the C" 5Pi(ui) state of N2 for both the (3-1) and (4-2) vibrational bands as well as the first observation of the v' = 4 vibrational level.

Lasing threshold reduction in grating-tuned cavities.

A new geometry for grating-tuned cavities that reduces optical losses from the gratings, lowers the lasing threshold, and enhances the laser output is described and tested. We achieved these enhancements by feeding back into the cavity light that is normally lost through grating reflections. The new geometry is tested on two grazing-incidence dye laser cavities: one that resembles a Littman -Metcalf design and demonstrates the essential principle of the new arrangement, and one that introduces modifications necessary to allow single-longitudinal-mode operation without mode hopping over a tuning range of ~15 cm-1 .