The decay rate of the Hg 61P1 level was measured as a function of cold spot temperature (Hg density) and buffer gas pressure in cylindrical, sealed fused silica cells. The decay rates were obtained using a time-resolved laser-induced 185 nm fluorescence experiment with multi-step excitation. Cold spot temperatures from 25 to 100 °C were studied. The Hg densities for this temperature range and with no buffer gas yield the lowest possible decay rates due to radiation trapping with partial frequency redistribution. Decay rates with argon buffer gas pressures of 3 and 30 Torr were also studied. The results are in agreement with published data from a discharge afterglow experiment. Monte Carlo simulations of radiation transport in the cells, including the effects of hyperfine and isotope structure, the effects of foreign gas broadening, and partial frequency redistribution are compared to the experimental data. Reasonably good agreement is obtained, however there is evidence of quenching of Hg 61P1 atoms in collisions with ground state Hg and Ar atoms. An analytic formula for the fundamental mode trapped decay rate of the 61P1 level, which is applicable over a substantial region of parameter space, was devised from the Monte Carlo results.

No abstract

The decay rate of Hg 6 3P1 atoms, due primarily to the escape of trapped 254 nm resonance radiation, was measured as a function of both Hg and Ar density in cylindrical, sealed fused silica cells. Time-resolved laser-induced fluorescence at 254 nm was used to obtain the decay rates for Hg densities from 5 × 1013 to 7 × 1015 cm−3 (22–101°C cold spot temperatures) and Ar densities from 0 to 9.7 × 1017 cm−3 in a cell of inner radius 1.05 cm. These new experimental data are compared to Monte Carlo results from a highly realistic code for simulating radiation trapping. This code includes Voigt profiles from a combination of Doppler, resonance, buffer gas and radiative line broadening, as well as hyperfine and isotopic structure with proper collisional redistribution. Upper limits on the rate constants for the quenching of Hg 6 3 P1 atoms by collisions with ground level Ar and Hg atoms were derived. Additional Monte Carlo simulations covering cell radii from 0.1 to 3.0 cm were performed. A broadly applicable engineering formula is derived from this study, which predicts the Hg 6 3P1 decay rate from 254 nm resonance radiation trapping as a function of Hg and Ar densities and cell radius.

A highly sensitive multi-element optical absorption technique is used to measure the absolute column density of both CH, and CH radicals in a dc hollow cathode plasma-assisted chemical vapor deposition (CVD) system with CH, and H, used as the input gases. The plasma gas temperature is determined at different spatial points using the H, emission spectrum near 460nm. The spatial maps of the temperature and the radical densities provide information OA the chemical processes taking place in the discharge. The CH, and CH radical density measurements made in the dc discharge system are compared with similar measurements made in a hot filament CVD system. The [H]/[H,] ratio is derived from the CH, and CH densities using an analysis based on partial thermodynamic equilibrium of the single carbon hydrocarbon abstraction reactions.