Threshold ionization spectroscopy of H₂O, HDO and D₂O and low-lying vibrational levels of HDO⁺and D₂O⁺

Abstract

Rotationally resolved photoelectron spectra of jet-cooled H 2 O, HDO and D 2 O have been recorded near the origin of thẽ X + ←X photoionising transition following single-photon ionization using the complementary techniques of mass-analysed threshold-ionization (MATI) and pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy. A gas mixture of H 2 O, HDO and D 2 O with Ar was obtained by mixing H 2 O ( ) and D 2 O ( ) in a reservoir and bubbling Ar gas through the mixture. To unambiguously assign the photoelectron bands to H 2 O, HDO or D 2 O, the PFI-ZEKE photoelectron spectra of the mixture were compared to MATI spectra and to spectra of H 2 O. Analysis of the rotational structure of the origin bands (HDO and D 2 O and of the transitions to the (010), (020) and (100) levels of D 2 O + and the first excited level of the O-D stretching mode of HDO + provided new information on the photoionization dynamics of water and the energy level structure of HDO + and D 2 O + . IntroductionWater (H 2 O) and its cation (H 2 O + ) are prototypical small molecules [1] and play an important role on earth and in the universe. Studies of H 2 O, HDO and D 2 O by vacuum-ultraviolet photoelectron and photoionization spectroscopy provide information on their interaction with short-wavelength radiation, on their photoionization dynamics and on the energy-level structure and dynamics of the cations [2-16]. The valence-shell photoionization of water, either in a single-photon process from theX 1 A 1 ground state or in multiphoton processes through electronically excited states, has provided access to a wide range of rovibrational levels of theX + 2 B 1 andà + 2 A 1 states of the cation, which are degenerate in linear (D ∞h ) configurations and subject to the Renner-Teller effect [17][18][19]. Whereas H 2 O + in the first excited state is quasilinear, the equilibrium geometry of the ground cationic state is bent and similar to that of the ground state of the neutral. Consequently, many more vibrational levels of theà + 2 A 1 state are accessible by photoionization from the ground state of the neutral than is the case for theX + 2 B 1 state [2,4,5,12,15,16].The vacuum-ultraviolet (VUV) photoelectron spectrum of theX + 2 B 1 ←X 1 A 1 photoionising transition of water thus consists of only a few vibrational bands, i.e., a strong origin band and weak and short progressions in the bending (0, v + 2 , 0) and symmetric stretching (v + 1 , 0, 0) modes [4,12,15,16]. The weakness of the bands associated with

Photoelectron Spectroscopy of Liquid Water with Tunable Extreme-Ultraviolet Radiation: Effects of Electron Scattering

“…The AVIEs of gas-phase water do not significantly vary with the photon energy, supporting the validity of the Condon approximation. The measured ionization energies moreover agree well with those previously reported (see, e.g., refs , , and ). The corresponding vertical ionization energies are indicated as violet diamonds, and the result of a Gaussian fit to the photoelectron spectra from ref as a red triangle.…”

Full-dimensional theoretical description of vibrationally resolved valence-shell photoionization of H2O

“…These measurements extend earlier high-resolution threshold photoelectron spectroscopy studies of H 2 O (see Ref. 29 and references therein) with which a direct comparison with the present theoretical calculations is difficult. The good agreement between theory and the present experiment validates the theoretical treatment and shows that the bending and the two stretching modes (symmetric and antisymmetric) play a crucial role in the measured spectra.…”

High-resolution photoelectron-spectroscopic investigation of the H2O+ cation in its electronic state

“…The line positions closely correspond to theà + Π(080) rotational level structure determined from theà + −X + band system by Lew [3] (see Table 2) and are also in good agreement with thẽ A + Π(080) level positions calculated by Brommer et al [18]. The term values listed in Table 2 were determined by adding the ground-state rotational energies to the field-corrected transition wavenumbers observed in the PFI-ZEKE photoelectron spectra and subtracting the adiabatic ionization energy of theX + −X transition (i.e., 101 766.3(10) cm −1 [14]).…”

“…This degeneracy is lifted by the Renner-Teller effect as soon as the molecule bends, the coupling being mediated by the bending mode ν + 2 . This pair of states and the vibronic interaction between them have been the object of extensive work, both experimental [1][2][3][4][5][6][7][8][9][10][12][13][14] and theoretical [15][16][17][18][19]. The most extensive set of high-resolution spectroscopic information on the X+ and Ã+ states of H 2 O + have been obtained from spectra of the Ã+ − X+ band system in the visible and near infrared ranges of the electromagnetic spectrum [1,3,10,11].…”