Time-of-Flight Mass Spectrometry for Time-Resolved Measurements: Some Developments and Applications

摘要

In this paper, the time resolution for kinetic studies of reactions with mass spec-trometric detection is characterized in detail, and it is shown how this allows faster kinetic processes to be determined. The time-resolved technique used pulsed laser photolysis to initiate reaction and a time-of-flight mass spectrometer (TOFMS) to monitor progress, where the reactant gas was sampled by a sampling orifice and photoionized using pulsed, laser vacuum ultraviolet light before being analyzed by the TOFMS. Characterization of this setup has been carried out to identify the parameters that affect the time for "sampling," which limits the fastest reactions that can be measured. A simple mathematical equation has been developed to correct for "sampling" delays (k_(ampling) ～ 25,000 s~(-1)), which extends the range of rate coefficients to be measured in a kinetic mass spectrometry reactor to k' < 7000 s~(-1). This method could be applied to any other kinetic mass spectrometry system where k_(sampling) can be measured; an important advantage since it allows the study of reactions over a wider range of conditions (e.g., larger concentrations of reagents/products can be used to minimize the contribution from wall losses). The system can produce reliable kinetic data whether monitoring reactant decay or product growth evert when the reaction and sampling processes are occurring on a similar timescale (k' < 7000 s~(-1) ). Reproducible and reliable kinetic data have been obtained for the following reactions: SO + NO2→ products (R1), ClSO + NO2 → products (R2), where SO and ClSO were monitored under pseudo-first-order conditions, and HCO + O2 → CO + HO2 (R3), where CO was monitored by a (1 + 1) resonance enhanced ionization multiphoton ionization (REMPI) scheme with HCO reacting under pseudo-first-order conditions. The limitations and potential developments of this setup are described.