(0 0 0) and (0 1 0) States of [formula omitted]: analysis of rotational transitions in hot emission spectrum in the [formula omitted] region

Abstract

The far-infrared emission spectrum of water vapour have been recorded at temperature 1370 K in the range 400–850 cm −1 at resolutions (FWHM) 0.0055 cm −1 . The measurements have been done in a fused quartz cell with an effective length of hot gas of about 60 cm. Among about 200 lines assigned to the H 2 18 O isotopomer 106 lines have not been reported in previous studies. These newly measured lines correspond to higher values of rotational quantum numbers compared to previous determinations: J max=18 and K a ( max) =17 for the (0 0 0)←(0 0 0) band and J max=15 and K a ( max) =11 for the (0 1 0)←(0 1 0) band. Estimated accuracy of line position measurements is 0.0005 cm −1 . To our knowledge rotational transitions within an excited bending state have been measured for the first time for H 2 18O. An extended set of experimental rotational energy levels for (0 0 0) and (0 1 0) vibration states including all previously available data has been determined. A data reduction has been done using the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.0009 cm −1 for 305 rotational levels of the (0 0 0) state and 0.0007 cm −1 for 198 rotational levels of the (0 1 0) state. A comparison of the observed data with the best available predictions from the molecular electronic potential energy surface [J. Chem. Phys. 106 (1997) 4618] and isotopic effects for rotational levels of (0 0 0) and (0 1 0) states are discussed.