A SELECTED-ION FLOW TUBE-LASER INDUCED FLUORESCENCE INSTRUMENT FOR VIBRATIONALLY STATE-SPECIFIC ION-MOLECULE REACTIONS

A selected ion flow tube apparatus is coupled with laser induced fluorescence (LIF) detection for the selective monitoring of ion vibrational states and their reactions. Mass selected ions are injected into a flow tube with a venturi inlet using He carrier gas. A 200 Hz dye laser system provides sensitive LIF detection of the injected ions at densities as low as 1 x 10(5) cm-3 for N2+. The rotational temperatures of the N2+ ions are estimated to be almost-equal-to 300 K using the LIF detection, while the vibrational temperatures can be high and may be varied by the injection potentials. Vibrationally state-selected ion-molecule reactions of N2+ (v = 0, 1, and 2) are studied with N2, Ar, and O2 at thermal kinetic energies (E(lab) < 0.1 eV), where translation-to-vibration energy transfer is negligible. Isotopically specific charge-transfer reactions of N-15(2)+ (v) with N-14(2) are also studied. The ability to mass select ions and characterize their vibrational states and those of their reaction products allows novel studies of state-to-state ion chemistry.