Laser-induced fluorescence (LIF) measurements of OH(X 2Π) production following electron impact on water have been carried out over an energy range from threshold to 300 eV. Data have been made absolute using existing measurements of OH(X) production via dissociative attachment. The cross section reaches a maximum value of 2.1×10−16 cm2 at an energy of 75 eV. Dipole-allowed processes are shown to dominate the production of OH(X) particularly via the A(1B1) repulsive state, though significant population of higher rotational levels is demonstrated, indicating the relevance of other channels as in photodissociation.
An atom trapping technique for determining absolute, total ionization cross sections ͑TICS͒ out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the "trap loss" technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs 6 2 P 3/2 state between 7 eV and 400 eV. CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region ͑Ͻ11 eV͒ where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.
Total fragmentation of H 2 O and D 2 O has been studied as a function of incident energy over the range from threshold to 325 eV. A small subset of possible dissociation channels has been selected by making use of a novel solid xenon matrix detector which is selectively sensitive to O( 1 S) metastable atoms. O-fragment kinetic energies and appearance potentials have been measured and significant isotopic effects are observed. Within the errors of the measurements the cross section for O( 1 S) production from H 2 O is the same as that from D 2 O. The cross sections reach a maximum value of 1.5 × 10 −18 cm 2 at 100 eV incident electron energy.
Vacuum-ultraviolet emissions following the dissociative excitation of H 2 S by electron impact at 100 eV incident energy have been measured. The absolute photoemission cross sections are presented over the wavelength range from 94 to 170 nm and the H, SI, or SII transitions producing the features identified. The measured cross section of the Lyman-␣ emission at 121.6 nm for an electron-impact energy of 100 eV is ͑9.79Ϯ 0.67͒ ϫ 10 −18 cm 2 . Excitation functions of the dominant H and SI emission lines are shown for electron-impact energies from threshold to 300 eV. We study the near-threshold region of the excitation functions and use the measured threshold energies to identify the dominant fragmentation channels.
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