Photoionization of rotationally cooled H2O and D2O in the region 650–990 Å

Room temperature and rotationally cooled relative photoionization cross sections for H2O and D2O were determined in the wavelength region 650–990 Å with a wavelength resolution of 0.06–0.11 Å (∼7–12 cm−1 ); the spectra were normalized to the absolute photoionization cross sections determined by Katayama et al. [D. H. Katayama, R. E. Huffman, and C. L. O’Bryan, J. Chem. Phys. 59, 4309 (1973)] with lower resolution. A rotational analysis of the Π subbands in the (0,6,0) and (0,8,0) bands of the (Ã 2A1)3db11B1←X̃1A1 Rydberg transition determined the symmetry of the upper state; in addition, the series was extended to higher principal quantum numbers. The analysis of these and other bands was made difficult both by the large natural linewidths of the rotational transitions and by the absence of transitions to rotational levels with N′≳3.