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Abstract: Using a cryogenic cell and a series of Distributed Feed Back (DFB) diode lasers, new high resolution spectra of methane have been recorded at 80K and room temperature by differential absorption spectroscopy (DAS) between 6717 and 7589cm−1 (1.49–1.32μm). The investigated spectral region corresponds to the very congested icosad, which is not tractable by theory. Empirical lists of 19,940 and 24,001 lines were constructed from the 80K and room temperature spectrum, respectively. The room temperature list adds about 8500 features to the empirical list of 15,375 lines at 296K adopted in the HITRAN database from the original work of L. Brown (Brown, L. Empirical line parameters of methane from 1.1 to 2.1μm. JQSRT 2005;96:251–70). A number of relatively strong CH4 lines located near strong water lines were found missing in the HITRAN line list. The improved sensitivity allowed adding more than 7000 lines to our previous list of about 12,000 transitions at 80K (Campargue A, Wang L, Kassi S, Mašát M, Votava O. Temperature dependence of the absorption spectrum of CH4 by high resolution spectroscopy at 81K: (II) The Icosad region (1.49–1.30μm). JQSRT 2010;111:1141–51). In order to facilitate identification of the transitions of the different methane isotopologues present in “natural” isotopic abundance, spectra of highly enriched CH3D and 13CH4 samples were recorded with the same experimental setup, both at room temperature and at 80K. From the variation of the line strengths between 80K and 294K, the low energy values of about 12,000 transitions were determined. They allow accounting for the temperature dependence of 84 and 93% of the methane absorbance in the region, at room temperature and 80K, respectively. As a result, we provide as supplementary material two complete line lists at 80K and 294K, including CH3D and 13CH4 identification and lower state energy values. [Copyright &y& Elsevier]

Abstract: In spite of its low isotopic abundance in methane (about 5×10−4), CH3D contributes greatly to the very weak absorption in the 1.58μm methane transparency window. This methane window deserves to be characterized in details because it is important for planetary applications in particular for Titan and the giant planets. In this work, we recorded the CH3D spectrum by high sensitivity differential absorption spectroscopy (α min ≈5×10−8 cm−1) both at room temperature and at 81K. A list of more than 9000 lines was constructed from the 81K spectrum for the 6099–6530cm−1 region. In order to get the temperature dependence of the line intensities, the low energy values have to be determined. The rovibrational assignments available in the literature provide low energy values for about 380 strong transitions of the region. This is insufficient to characterize the temperature dependence of the CH3D absorption between 6200 and 6400cm−1. In this interval, a list of 5500 lines was constructed from the room temperature spectrum. The empirical energy values of the transitions were derived from the ratio of the intensities at 81K and 294K. The exact and empirical lower state energies included in the final line lists provided as , allow for accounting for the temperature dependence of the CH3D spectrum in the entire 6099–6530cm−1 region. Our measurements have been compared to the spectroscopic parameters and assignments available in the literature in particular those adopted in the HITRAN database. Improvements and corrections are proposed for the wavenumber calibration and for some lower state energies. [Copyright &y& Elsevier]

Abstract: The very weak absorption spectra of 18O3 and 16O3 have been recorded between 7700 and 7920cm−1 by high sensitivity cavity ring down spectroscopy (α min ∼10−10 cm−1). The upper limit of the investigated region is only 6% below the dissociation energy. The spectrum consists in the superposition of very weak vibrational bands and unexpected broad absorption features which dominate in the case of the 18O3 isotopologue. From recordings at temperatures ranging from 294 to 354K, the broad features were identified as due to the 3A2(000)–X1A1(110) hot band. The rovibronic levels of the 3A2(000) state are predissociated and the widths of the corresponding lines range from 0.02 to at least 0.5cm−1. [Copyright &y& Elsevier]

Abstract: Helium broadening coefficients for the R(10) and the P(2) lines in the ν3 band of 13CO2 have been measured over a large range of temperature (70K–300K). Helium pressure shifts for the R(10) line at several temperatures between 100K and 300K have also been determined. These measurements were obtained with a cold Herriott cell, using the collisional cooling technique to reach the lowest temperatures. They provide an extended dataset for the temperature dependence of widths and shifts. This dataset was compared to theoretical He-broadening coefficients combining quantum scattering calculations and the latest potential energy surface for the system He–CO2 from Korona et al. [T. Korona, R. Moszynski, F. Thibault, J.-M. Maunay, B. Bussery-Honvault, J. Boissoles, P.E.S. Wormer, J. Chem. Phys. 115 (2001) 3074–3084]. [Copyright &y& Elsevier]

Highlights: [•] First complete jet spectrum in the lower icosad region of methane (7040–7380cm−1). [•] Determined empirical E″ and J″ using 28K/81K two-temperature intensity analysis. [•] Identification of 16 R(0) transitions in the studied spectral range. [ABSTRACT FROM AUTHOR]