REMPI spectroscopy and predissociation of the C̃1B1(v = 0) rotational levels of H2O, HOD and D2O

Abstract

Rotational analysis of the (2 + 1) resonance enhanced multiphoton ionization (REMPI) spectrum of the C(1)B(1) Rydberg state of the water isotopomers H(2)O, HOD and D(2)O is reported. Spectroscopic parameters for the v = 0 vibrational level of the C(1)B(1) state of the mixed isotopomer HOD are derived and its spectra are accurately simulated for the first time using the PGOPHER program. Simulation of two photon spectra of the C(1)B(1)-X(1)A(1) transition of HOD requires two transition moments, and the ratio of these is determined and explained by a simple geometrical model. Optimal transitions for state-selective detection of low energy rotational states are identified for all three molecules. Analysis of the linewidths in the present work, combined with previous work [H. H. Kuge and K. Kleinermanns, J. Chem. Phys., 1989, 90, 46-52; K. J. Yuan et al., Proc. Natl. Acad. Sci. U. S. A., 2008, 105, 19148-19153; M. N. R. Ashfold et al., Chem. Phys., 1984, 84, 35-50; G. Meijer et al., J. Chem. Phys., 1986, 85, 6914-6922.], suggests that while a simple ⟨J(a)'(2)〉-dependent model for heterogeneous predissociation of the C(1)B(1) Rydberg state accounts for much of the quantum number dependence, it is not sufficient for describing the predissociation in any of the three isotopomers. The component of the linewidth due to the homogeneous predissociation attributed to predissociation of the C(1)B(1) by the Ã(1)B(1) state was found to be significantly narrower than in previous work, indicating a longer lifetime of the C(1)B(1) Rydberg state. The current work provides the basis for on-going studies of rotational energy transfer in the mixed isotopomers of water using the velocity map imaging technique.

State-to-state differential and relative integral cross sections for rotationally inelastic scattering of H2O by hydrogen

“…23 , 24 , 17 Here we use prime character, ' , to note the associated quantum numbers in the C 1 B1 Rydberg. Consequently, the choice of REMPI transitions with a smaller value of Ka' results in narrower REMPI lines, enabling the detection of single rotational states (J"Ka"Kc") of nascent H2O after collisions .…”

“…17 A tunable dye laser system (Lambda Physik ScanMate) pumped by the third harmonic of a pulsed Nd:YAG laser (Contiuum Powerlite 9010) was used for the ionization process. Coumarin 307 dye was used to produce dye laser wavelengths around 496 nm.…”

“…17 Moreover, the rotational states (J) of hydrogen before and after inelastic scattering were examined by several different REMPI detection schemes. 20 , 21 The extracted DCSs from the experiments are compared with close--coupling calculations performed with state--of--the--art potential energy surfaces.…”

“…We use here the notation JKaKc for the rotational states of H2O, with total angular momentum J and the quantum numbers Ka and Kc are the values for the projection of J on the a and c rotation axis. 17 In this computation, the rotational constants of H2O were taken at 27.88063134, 14.52176959, and 9.277708381 cm --1 . In addition, for the H2 (D2) molecule, the symbol J is used to denote the rotational state.…”

Communication: Mapping water collisions for interstellar space conditions

“…10. Full details of the apparatus 11 and the nascent water laser ionization detection method 12 will be given in forthcoming publications. In short, molecular beams of water and H 2 or He are crossed at 90°, where H 2 O and H 2 are prepared predominately in their lowest possible rotational states.…”