Mass-Spectrometric Study of Ions at Near-Atmospheric Pressure. III. The Alpha Radiolysis of Methane

Abstract

The ion—molecule reactions occurring in the alpha‐particle radiolysis of methane have been studied in a mass spectrometer under near‐conventional radiolysis conditions (1–160 torr pressure and a few milliseconds ion reaction time). Comparison of the observed high intensities of CH₅⁺ and C₂H₅⁺ at 1 torr with spectra obtained previously with conventional microsecond reaction times shows that the reactions of CH₅⁺ and C₂H₅⁺ with methane are very slow (k<10⁻¹⁵ cc molecule⁻¹·sec⁻¹). At higher pressures C_nH⁺_2n−1, C_nH⁺_2n+1, and C_nH⁺_2n+3 are observed with $\text{n≦6}$ . The addition of trace concentrations of normal and deuterated hydrocarbons helps to elucidate some of the reactions involved. The ions observed in the presence of traces of deuterated alkanes present a complete confirmation of reactions proposed earlier by Ausloos whose work was based on neutral product studies in α‐radiolyzed methane and deuterated alkanes. The present work with additives shows that impurities at concentrations of 1 ppm affect the course of the ionic reactions in the radiolysis of methane at near‐atmospheric pressures. The origin of the ions observed in the present work in ``pure'' methane at pressures above 10 torr is therefore uncertain. These ions are probably largely due to impurities.