OCS at low pressure was photodissociated at 248 nm. It was shown by two photon laser induced fluorescence (LIF) that the concentration of the S(1D) atoms produced decays with time due to collisions with undissociated OCS molecules. In contrast, the S(3P) atom concentration rises from zero or nearly zero to a maximum and then subsequently decays. The S(1D) atoms react with OCS molecules to give S2 (X 3Σg), S2(a 1Δg), and S(3P). The rotational and vibrational distribution of the diatomic products was studied by LIF. The diabatic product S2(X 3Σg) was entirely in the v=0 state and was rotationally cold. The adiabatic product S2(a 1Δ) was probed in the v=1 state and had a fairly narrow non-Boltzmann type rotational distribution peaking at J=65. We speculate that the reaction takes place through a C2v COS2 intermediate. The adiabatic and diabatic reactions are characterized by sequential and concerted C–S bond breaking, respectively.
The a1Πg(v′=0.1)←X1Σ+g(v″=0) transitions in N2, part of the Lyman–Birge–Hopfield bands, have been seen by two-photon absorption detected by VUV fluorescence. Fluorescence was observed over a pressure range from 5 m Torr to 10 Torr. From the lifetime decrease with pressure at low pressure, quenching rate constants were determined, which are equivalent to cross sections in the range of 2.6×10−16 cm2. At higher pressures a slow decay was observed that is interpreted as being due to the a′ state which acts as an energy reservoir with a pressure dependent decay constant. We anticipate that laser-induced fluorescence will be a useful scheme for measuring ground state rotational and vibrational populations for the nitrogen molecule.
A KrF excimer laser using an all solid state Pulse Power Modulator (PPM) has been studied. This PPM configuration replaces the commonly used thyratron switch with a Silicon Controlled Rectifier (5CR) switch combined with a pulse compression-voltage multiplication circuit. Use of this PPM has extended the useful chamber life of a line-narrowed KrF excimer laser from 1.5 billion to 2.5 billion pulses. Broadband KrF laser performance, optimized for mirror based scanner systems, has also been investigated. A minimum broadband chamber life of 5 billion pulses has been demonstrated with this solid state PPM. While a thyratron-based PPM exhibits an expected lifetime of 3 billion pulses, the solid state PPM used in these experiments has been operated for greater than 6 billion pulses without any decrease in performance. Since 72% of the replacement parts cost for the ELS-4000D line-narrowed excimer laser is due to periodic chamber and PPM replacement, significant cost of ownership reduction is realized by extending the lifetime of the chamber and the PPM.
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