J. S. Holloway

High resolution absorption spectroscopy of NO2

Abstract The absorption cross-section of NO 2 has been measured above the 3979 predissociation limit in the region of 3920 and 3950 and in the discretely structured areas around 4112 and 4140 . Spectra were taken in a dual-beam arrangement using a tunable, pulsed dye laser with 0.05 bandwidth (FWHM). This represents an improvement of at least a factor of three over the resolution employed in previous studies. Below 3979 , the spectra are continous with occasional diffuse rotational lines superimposed. The spectra taken above 4100 reveal a wealth of structural complexity. We report here absolute cross-sections taken at 300 . The work above 4100 was also performed at 250 . Only slight variations in the measured cross-sections are observed between these two temperatures.

Measurements of XeF ground state dissociation and vibrational equilibration

The removal rates of the lower levels of the XeF(B→X) excimer laser transitions strongly affect the overall efficiency of the E‐beam‐pumped devices. We have deduced the removal rates of XeF(X,v) in argon, helium, and neon by measuring the populations of vibrational levels v=0, 1, 3, and 4 formed by the photolysis of XeF2. The time history of each vibrational population is monitored with a cw tunable dye laser tuned to an absorption feature of the selected vibrational/rotational level. The studies show a rapid vibrational relaxation followed by a common decay rate of the coupled vibrational levels. Helium and neon were found to remove these levels with the same rate coefficient of (2.0±0.2)×104 (s Torr)−1 at room temperature. The corresponding rate coefficients for argon were larger by about 25%. The removal rate coefficients increased with temperature in the range of T=23–95 °C. The rate coefficient for the vibrational excitation of v=0 by helium was measured to be (3.6±0.7)×105 (s Torr)−1 at room tempera...

Photodissociation of XeF2 at 193 nm

Abstract The absorption coefficient of XeF 2 has been measured at 193, 206, and 253 nm. The measurements have been compared with those of Black et al. and Jortner et al. The present measurements of XeF 2 absorption at 193 and 253 nm appear to resolve the discrepancy in those absorption measurements. Adjusting the data of these two previous investigations to match our values at these two wavelengths brings the two sets of measured absorption coefficients into agreement in the overlapping wavelength interval, 203–210 nm. We determined experimentally that one molecule of XeF 2 is dissociated for each photon absorbed at 193 nm.

Vibrational relaxation and electronic quenching rate coefficients for BiF(A0+,v’) by SF6

We have extended our kinetic data base for the A state of BiF to include SF6 as a collision partner. By applying a four level finite difference fitting routine to time‐resolved fluorescence traces from v’=0–3, we have obtained rate coefficients for electronic quenching, and for vibrational relaxation within the A‐state manifold. As was the case for our previous results in He and Ar, electronic quenching is slow in comparison to radiative decay. Vibrational relaxation does not show a simple v’ dependence, but rather, for the levels examined, increases markedly for higher v’. Our results confirm the suitability of SF6 as a bulk diluent in the proposed NF/BiF chemical laser system.

Gas Phase UV Photochemistry Of NF 2 Dynamics And Kinetics Of NF(X 3 ∑) And NF(A 1 Δ) Radical Products And Direct Measurement Of The H + NF 2 Reaction Branching Ratio

In a series of experiments we have investigated the NF2 UV photolysis product distributions, the kinetics of those products, and the reaction of the parent NF2 with atomic hydrogen. Our experiment utilizes a teflon coated photolysis chamber which can be heated (420 K) and in which we flow the reagent tetrafluorohydrazine (N2F4: 10% mixture in Ar). At the photolysis cell temperature, the N2F4 pyrolyzes (98%) to form 2NF2. An excimer laser (248 nm, 193 nm) or a tunable UV laser (frequency up converted Nd-Yag pumped dye laser) is used as the photolysis source. The Nd-Yag pumped dye laser in the visible also serves as a pump in the laser-induced fluorescence (LIF) studies of NF(X3∑). Two PMTs, are simultaneously used to detect the LIF from NF(X3∑) and fluorescence emission from NF(a1Δ). This capability allows us to simultaneously monitor both ground and excited state products following laser photolysis. Two computers are necessary for the experiment. The first monitors the LIF signal as a function of delay time between photolysis and probe laser, both laser energies, and the probe laser wavelength. The second computer is used to acquire data of the fluorescence emission as digitized by a fast transient recorder. We also monitor all gas mass flow meters, the cell temperature, and pressure.