A supersonic jet/resonance-enhanced multiphoton ionization/time-of-flight mass spectrum (SSJ/REMPI/TOF-MS) was measured for xylenols and ethylphenols. Sharp and intense peaks were observed in the REMPI spectrum of 2,4-xylenol, and the wavelength of the peak tentatively assigned to the 0-0 transition was the longest among xylenols and ethylphenols. These results suggest that 2,4-xylenol, designated as a Class II chemical substance in the Pollutant Release and Transfer Register (PRTR), can be measured sensitively and selectively even when numerous isomers are present in the sample.

A pair of concentric capillaries was developed to mix helium, which was used as the carrier gas for gas chromatography, with argon for efficient molecular cooling by supersonic jet expansion. A simple instrument was constructed for the evaluation of nozzle diameter using the Hagen-Poiseuille equation. The effects of nozzle diameter, type of expansion gas, flow rate, and the distance from the nozzle to the observation region were investigated. Mixing argon gas with the carrier gas helium resulted in efficient molecular cooling from 30 to 10 K and the complete disappearance of the background signal from the multiphoton ionization spectrum. Consequently, the spectral selectivity was significantly improved and the nozzle was successfully applied to isomer-selective analysis of dichlorotoluenes. Since the dead volume in the nozzle was negligible, it was suitable as an interface for gas chromatography and supersonic jet/multiphoton ionization/mass spectrometry.

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A time-of-flight mass spectrometer was constructed for use in detecting negatively charged species induced by laser multiphoton ionization. Mass spectra, collected for a variety of compounds, contained several signal peaks. Their flight times were, however, an order of magnitude shorter than the values predicted based on the length of the flight region. To clarify this curious phenomenon, a simple molecule, namely, nitric oxide was measured for calibration of the flight times and for assignment of the signal peaks. A careful investigation led to a possible mechanism, in which the signals do not arise from negative ions but arise from electrons generated at the surface of the repeller electrode by collisions of positive ions that are formed by multiphoton ionization of the analyte in a molecular beam.