Radial variations of the Hg(63P0,1,2) densities are measured in a low-pressure Hg-Ar discharge and the results are compared with a model. The 34-mm-diam discharge tube is operated in the vicinity of 400-mA current, 6.4-mTorr Hg pressure, and 2.81-Torr Ar pressure. A tunable dye laser beam passes axially through the discharge tube, and densities are measured using both a saturated absorption technique and an interference technique. The model incorporates continuity equations for Hg excited and ionic states, and a two-temperature approach to parametrizing the electron energy distribution function. The shapes of the radial density distributions of the various species are predicted rather than assumed. Considerable attention is given to the role of tail electrons above the energy threshold for Hg inelastic scattering. Theoretical considerations and the measured variations of the 63P0 and 63P2 metastable densities suggest that the tail electron temperature is lower near the wall than at the center of the discharge.

Quantum. st~tes of N0 2 are selected. and then photodissociated by resonant two-photon photoexcItatlOn. The total photolYSIS energy is scanned over a region from 50 cm -1 below to 300. cm-I abov~ the threshold for ~roduction ofNO(X 2 n) + O(ID). This channel yielding eX~Ited ~xygen IS observed to domInate the production of vibrational ground state NO. ~I~tO~IC product J an~ A ~oublet state distributions are probed by resonant two-photon lOnIzatIon. The photodIssocIation cross section for production of specific NO quantum states is found to be structured in the photolysis wavelength. This structure is assigned to intermediate resonance in the two-phot?n photolysis. Rotational structure is identified in this pattern, and confirmed by separate optIcal-UV -double resonance spectroscopy using the same intermediate states i~ co~b~nation wit~ levels of the 3pu 2l:u+ Rydberg state of N0 2 • Though p~otodIsSOCIatIOn dynamIcs are found to be a very sensitive function of photolysis wavelength, dIfferent wavelengths that promote different transitions through the same intermediate state yield very similar dynamics. The existence and apparent patterns of photoselection in the product state dynamics are discussed in the light of recent theoretical developments incorporating electronic degrees of freedom in state-to-state photofragmentation.

Two laser-based techniques are used to derive radial density distributions and absolute densities for the three 63PJ excited states of mercury in the positive column of a low-pressure Hg-Ar dc discharge. In the saturated laser absorption (SLA) method, a pulsed dye laser, traversing the discharge axially, is scanned through one of the 63PJ→73S1 transitions. At high laser powers the power absorbed from the beam on resonance approaches a constant saturated value directly proportional to the number density of Hg atoms in the 63PJ state selected. On-axis absolute density estimates and radial distribution results are presented for the three states at several discharge conditions. The hook method, a well-known interferometric technique, more accurately establishes the absolute densities on axis, and several off-axis measurements are compared with SLA results.

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