An empirical line list for methane in the 1.25μm transparency window

International audienc

The absorption spectrum of water was recorded by ICLAS between 13540 and 14070 cm-1.

International audienceThe absorption spectrum of water vapor has been investigated by Intracavity Laser Spectroscopy (ICLAS) between 13540 and 14070 cm-1. This spectrum is dominated by relatively strong transitions of the 4 polyad of vibrational states. The achieved sensitivity – on the order of min~10-9 cm-1 – has allowed one to newly measure 222 very weak transitions with intensities down to 5×10-28 cm/molecule at 296 K. 50 new or corrected H2 16O energy levels belonging to a total of 13 vibrational states could be determined from the rovibrational analysis based on variational calculations by Schwenke and Partridge. The previous investigations in the region by Fourier Transform Spectroscopy were critically evaluated and used to construct the best to date set of energy levels accessed by transitions in the considered region. All the rovibrational transitions reaching these upper energy levels and having intensities larger than 4.0×10-28 cm/mol were calculated. In the resulting line list, the positions at the level of experimental accuracy were augmented with variational intensities leading to the most complete line list for water in normal isotopic abundance in the 13500-14100 cm-1 region

ICLAS of HDO between 13020 and 14115 cm-1

International audienceThe high resolution absorption spectrum of monodeuterated water, HDO, has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) in the 13020-14115 cm-1 region dominated by the 43 band. The achieved noise equivalent absorption (min~ 10-9 cm-1) allowed detecting transitions with line strengths as small as 2×10-27 cm/molecule which is about 10 times lower than the smallest line intensities previously detected in the region. The rovibrational assignment of the spectrum was based on the results of the variational calculations of Schwenke and Partridge (SP) as well as recent calculations using a new potential energy surface performed by Voronin, Tolchenov and Tennyson (VTT). 2157 transitions involving 21 upper vibrational states were assigned to HD16O while only four bands were previously reported in the region. A set of 157 new energy levels could be derived. It includes rotational levels of several highly excited bending states, in particular the (0 11 0) pure bending state. For some states like the (103) and (023) Fermi dyad, effective Hamiltonian modelling was needed to establish the vibrational assignments of some rotational levels. VTT calculations were found to significantly improve SP results, the rms deviation of the calculated and observed energies being decreased from 0.23 to 0.06 cm-1. Finally, 79 transitions of the 43 band of the HD18O isotopologue were assigned, leading to the derivation of 48 levels which are the most excited energy levels reported so far for this isotopologue