An ion cyclotron resonance spectrometer as a gas chromatographic detector: Measurement of momentum transfer collision frequencies

Abstract

The momentum transfer collision frequencies (ξ/ n) of 39K + with the three isomers of difluorobenzene are reported. The measurements have been done using ion cyclotron resonance techniques. Conventional linewidth measurements gave (ξ/ n) para = 1.71 ± 0.08 × 10 −9, (ξ/ n) meta = 2.18 ± 0.11 × 10 −9, and (ξ/ n) ortho = 2.79 ± 0.14 × 10 −9 cm 3 molecule −1 s −1. A method for measuring relative momentum transfer collision frequencies at resonance is described. The method involves coupling a gas chromatograph to the ion cyclotron resonance (ICR) spectrometer. Using this method it was found that (ξ/ n) ortho /(ξ/ n) para = 1.63±0.08, (ξ/ n) ortho /(ξ/ n) meta = 1.24±0.02, and (ξ/ n) meta /(ξ/ n) para = 1.32±0.07. The significance of the good agreement between the linewidth measurements and the measurements at resonance is discussed. The measurements are compared with those of Su and Bowers for the momentum transfer collision frequencies of 35Cl − with the difluorobenzene isomers. It is concluded that the momentum transfer rate constants are not affected significantly by a change in the sign of the ionic charge. The measurements are also compared with theory and found to agree with momentum transfer collision frequencies determined from a potential of the form Ar −8 - Br −6 - α e 2/2 r 4 + E ψ where the third term is the ion-induced dipole term and the fourth term is a statistically averaged ion-dipole term. The effect of ion/molecule reactions on the GC-ICR method and possible analytical applications of the method are discussed.