Isotope-selective IR multiphoton dissociation of CHClF2 in the presence of NO2

2 to the CHClF₂/He mixture irradiated by a Q-switched CO₂ laser leads to oxidation of the dissociation product according to the reaction: CF₂+NO₂→COF₂+NO. The resulting COF₂ with a ¹³C content near 50% is easy to convert to CO₂ or CO for further enrichment by a nonlaser process. We measured the dependence of the fraction of dimerised CF₂ on NO₂ pressure p_NO2 and the amount of NO₂ required to suppress dimerisation on the dissociation yield. Both agree with a kinetic model using known rate constants. For the range of the dissociation parameters (¹³CF₂ yield of 10% per pulse, isotope selectivity of 130) of practical interest, 95% of the CF₂ produced is oxidized at p_NO2≈1/2p_CHClF2. In the absence of NO₂, major (20%–35%) losses of CF₂ at the metal walls of the irradiation system were observed. Addition of NO₂ suppresses them. For comparison, we also used O₂ as a scavenger in CHClF₂ dissociation. NO₂ is by orders of magnitude more efficient. Received: 21 January 1997/Revised version: 23 March 1997     

Formation of Xe12 by collision pair absorption at 158 nm

Pair absorption from colliding Xe atoms of the molecular fluorine laser radiation is reported. The absorption coefficient for this process at 300 K was found to be α = (4.32 ± 0.1) × 10^-9Torr^-2cm^-1. Fluorescence at 172 nm originating predominantly from the ${}^1\text{Σ}{}^{\mathrm{+}}{}_{\mathrm{u}}$ state of Xe¹₂ indicates that by this mechanism the Xe dimer laser can be pumped optically.     

Stimulated emissions from atomic iron generated by excitation of iron carbonyl

Single pass stimulated emissions from Fe1 were generated by transverse excitation of Fe(CO)₅, at submillibar pressures, by KrF pulses. Comparison of fluorescence spectra from iron carbonyl, with respect to frequency and time evolution, as developed under various excitation conditions demonstrated a high sensitivity of the states pumped to the manner in which the excitations were imposed.     

CARS spectroscopy of the NaH2 collision complex: the nature of the Na(32 P)H2 exciplex — ab initio calculations and experimental results

CARS (Coherent Anti-Stokes Raman Scattering) has been used to analyze the rovibronic state distribution of H₂ after collision with Na(3² P). New lines, which do not correspond to H₂ lines are observed in the CARS spectrum. The experiments point to the formation of a complex of Na(3² P)H₂ inA ² B ₂ symmetry. Ab initio calculations of theA ² B ₂ potential were performed. On this surface the vibrational spectra of the exciplex are evaluated. The observed lines can be attributed to vibrational transitions in the complex, in which combinational modes are involved. The connection of experimental and theoretical results indicates that a collisionally stabilized exciplex molecule is formed during the quenching process.     

Numerical simulation of the generation of gain switched laser pulses

Gain switched laser pulses with FWHM of 32 ps having an optical peak power exceeding 400 W are generated using low cost single heterostructure (SH) Fabry–Perot laser diodes. To examine and to optimize this effect in detail, a thorough physical device simulation is done. Maxwell's equations together with a simplified version of the Boltzmann transport equation (BTE) and various parameters like carrier recombination and material gain, form a coupled set of nonlinear, inhomogeneous partial differential equations, that are discretized using the finite difference scheme and solved selfconsistently.     

Comparative characterization of monodisperse platinum, palladium and nickel in a faujasite X matrix by dynamic oxygen chemisorption and electron microscopy

A comparison of particle size distributions from electron micrographs and oxygen chemisorption capacities on reduced platinum and palladium faujasite X confirms the existence of monodisperse metal phases of narrow aggregate size distribution and excludes a grape structure for the occluded metal particles. For reduced, monodisperse nickel faujasites a degree of reduction can be obtained by this comparison.

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