P. Crozet

Fourier transform spectroscopy of the 13Δg-b3Πu transition in 6Li2

Abstract The 1 3 Δ g - b 3 Π u transition of 6 Li 2 has been observed in collisionally induced fluorescence following (a) excitation of the C 1 Π u state by the ultraviolet lines of argon and krypton ion lasers and (b) single frequency double resonance excitation of the F 1 Σ g + state using a ring dye laser operating with DCM dye. Spectra were obtained at high resolution using Fourier transform spectrometers. Many lines are broadened and shifted because of predissociation of b 3 Π u by a 3 Σ u + ; the widths and shifts have been measured as a function of rotation and vibration. Several perturbations have been observed in the 1 3 Δ g state and are shown to be caused by interaction with the 2 3 Π g state. The data are reduced to molecular constants (Dunham coefficients), perturbations are analyzed, and the collisional mechanism responsible for excitation of the 1 3 Δ g state is discussed.

The spectrum of N2 from 4500 to 15700 cm−1 revisited with PGOPHER

Abstract Using a reference molecular atlas to ensure self-consistency of wavelength calibration is widespread practice. Boesch & Reiners (Astronomy & Astrophysics 582 A43 (2015)) reported a line list from a discharge of molecular nitrogen from 4500 to 11,000xa0cm−1 for this purpose. With a hollow-cathode discharge source, we have extended the experimental spectrum up to 15,700xa0cm−1, to include the range of Ti:sapphire lasers, since the density of N2 lines is greater than atomic atlases in common use. Recognizing that experimental conditions can vary, we have also analysed the spectra (comprising several B 3 Π g − A 3 Σ u + , B ′ 3 Σ u − − B 3 Π g , and u2005W3Δuu202fu202f−B3ΠgN2 bands) with standard Hamiltonians, so that any part of the discharge spectrum in the range 4,500–15,700xa0cm−1 can be simulated. Parameters are given to do this with the spectral simulation and analysis package pgopher . (C. Western, J. Quant. Spectrosc. Rad. Transf., 186 , 221 (2016)). The analysis also included high-level ab initio calculations of potential energy curves, transition moments and spin-orbit coupling constants and these were used in preparing the model, extending the potential range of applicability. The results are available in a variety of formats to suit possible applications, including the experimental spectrum in ASCII, a detailed line list with positions and Einstein A coefficients, and a PGOPHER input file to synthesize the spectrum at selectable temperature and resolution.

A CRDS sputter-source experiment to study MH radicals: application to NiH and NiD

ABSTRACT Signatures of metal hydride molecules appear in the optical spectra of cool stars. The observed spectra are used not only for identification of the molecule, but also to assess the abundance of the metal from which the molecule is composed, and to measure the strength of the magnetic field in which the molecule is immersed through the Zeeman splitting of individual spectral lines. Metal hydrides are short-lived radicals, often produced via an electrical discharge, and their steady-state concentrations in a sample are low. High-sensitivity probing techniques, like laser-induced fluorescence, are often appropriate, but (typically much less sensitive) absorption techniques are more useful to assess metal abundances. We describe here a cavity ring-down spectroscopy experiment, usually used to detect absorptions from stable molecules, to collect spectra with very high sensitivity and reproducibility from prototypical metal hydrides NiH and NiD. We have constructed an optical cavity of high finesse (F = 60,000) into which a sputtering source is inserted, and have employed optical fibre and a rigid mounting scheme to keep the ring-down mirrors in alignment during an experiment and between days. We compare our NiH/NiD absorption data with literature results, and highlight some of the strengths and weaknesses of this approach.