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We have developed a new technique for measuring the etch rate of polymer films under ablative photodecomposition condition obtained by absorption of the far-UV radiation of the excimer laser. The technique is based on the use of a quartz crystal microbalance interfaced with a microcomputer. It has good accuracy and thus provides precise evidence of a new feature of the etch curve for laser intensity right above the ablation threshold value. Further applications are proposed.

The recombination rate constant of the NH2 radical is measured by flash photolysis of ammonia as a function of total pressure from 0.3 to 1000 Torr of nitrogen. The recombination kinetics is third order between 0 and 20 Torr and the relative third body efficiencies of ammonia, nitrogen, and argon, determined in this pressure range, are 4.0, 1.0, and 0.4, respectively. The termolecular rate constant is, in the case of nitrogen, kUt^2 = 2.5(±50%) X 1012 M"2 s"1. The high pressure limiting value of ku(^) = 1.5(±50%) x 1010 M"1 s"1 is reached at about 1000 Torr of nitrogen. A low pressure limit & (0) = 8.5(±50%) X 10s M"1 s'1 is found when the pressure tends to zero. The disproportionation reaction of amino radicals seems to be the principal reaction at pressures lower than 1 Torr. No significant temperature effect is found either near the high pressure limit or at the low pressure limit. A small negative temperature coefficient (-!<£< -0.5 kcal/mol) is observed at 20 Torr of nitrogen, when the reaction is essentially termolecular. These results are discussed in connection with previous data concerning this reaction.

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