Microwave Cavity Spectroscopy

The influence of vibrational and collision energy on ion-molecule reactions was investigated by measuring the cross sections for reactions of NH3 created with varying degrees of excitation in the umbrella bending and symmetric stretching modes. Under these conditions, the three major product channels for the NH3CD3NH2 system are CD3NH2, CD2NH2 and CD3NH3. Two minor product channels correspond to NH3D and NH4. This reaction is found to be mode selective based on the reactivity of two isoenergetic vibrational states having differing concerted atom motions. The reaction of state selected ammonia ions with CD4 produces two major products, deuterium abstraction NH3D and collision induced dissociation NH2D. The reaction was found not to be mod selective. In the NH3THF system, four products were identified hydrogen abstraction NH4, charge transfer C4H8O, proton transfer C4H9O and an endothermic product corresponding to charge transfer with loss of H C4H7O. The branching ratios show a dependence on ammonia ion vibrational state In separate experiments, it was demonstrated that the new class of quantum cascade lasers that produce tunable infrared coherent radiation are well suited to cavity ring-down detection of ammonia. A detection limit of less than one part per billion was achieved.