A selected ion flow tube-laser induced fluorescence instrument for vibrationally state-specific ion-molecule reactions

Abstract

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 1×105 cm−3 for N+2. The rotational temperatures of the N+2 ions are estimated to be ≊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 N+2(v=0, 1, and 2) are studied with N2, Ar, and O2 at thermal kinetic energies (Elab<0.1 eV), where translation-to-vibration energy transfer is negligible. Isotopically specific charge-transfer reactions of 15N+2(v) with 14N2 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.