Rotationally resolved photoionization of H2O

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Abstract
A rotationally resolved one‐photon threshold photoionization spectrum of jet‐cooled water (H2O and D2O) has been obtained by pulsed field ionization of extremely high‐n Rydberg states. Observed spectral intensities for both vibrationless (0,0,0) and vibrationally excited (1,0,0) water cation show a strong propensity for ΔN=0, ±1 transitions. In contrast to earlier work on O2 and HCl, the lack of large ΔN transitions suggests that ionization occurs with only small angular momentum transfers between the core and photoelectron. The presence of both type A and type C ‘‘symmetric top’’ transitions varies from the conclusions of a recent MQDT analysis of H2O photoionization, which predicts only type C transitions. Rotational analysis of the spectra yields improved ionization potentials for both H2O and D2O. The ionization potential of the (1,0,0) vibrational level provides a direct measurement of the symmetric stretch fundamental in H2O+ which is in excellent agreement with an earlier indirect determination. Room temperature spectra are presented for ionization into the (0,0,0), (0,1,0), and (1,0,0) vibrational levels of H2O+.