High sensitivity ICLAS of H218O between 13 540 and 14 100 cm−1

Abstract The high resolution absorption spectrum of 18 O enriched water was recorded between 13 540 and 14 100 cm −1 by high sensitivity Intracavity Laser Absorption Spectroscopy (ICLAS). This spectral region corresponds to the relatively strong 4ν polyad. Four isotopologues of water (H 2 18 O, H 2 16 O, H 2 17 O, HD 18 O) are found to contribute to the spectrum. About 1800 H 2 18 O lines were assigned by comparison with variational calculations. Altogether, 855 accurate energy levels of H 2 18 O were determined from transitions attributed to 23 upper vibrational states, 342 of them being reported for the first time. New information includes 84 energy levels of H 2 17 O present with a 1.5% relative concentration in the sample and the rotational structure of the 4ν 3 band of HD 18 O at 13814.520 cm −1 . By comparison with variational calculations and with ICLAS absolute intensity values, a systematic overestimation by about 25% has been evidenced for the H 2 18 O intensity values included in the HITRAN database for the 12 400–14 520 cm −1 range.