Ion--molecule reactions in isopropanol: implications for its radiolysis

The photoionization of isopropanol ( i -PrOH) at 11.7 eV has been investigated in the NBS high pressure photoionization mass spectrometer over the pressure range 0.1 to approximately 200 millitorr. The major primary ion, CH 3 CHOH + , reacts with a total rate coefficient of 1.1 ±0.1× 10 -9 cm 3 /mole-cule-s to yield mainly ( i -PrOH)H + and CH 3 ( i -C3 H 7 )COH + . At pressures in excess of a few millitorr consecutive reactions of ( i -PrOH)H + and CH 3 ( i -C 3 H7)COH + were also detected, including the overall dehydration process ( i -PrOH ) H + + i -PrOH → H 2 O + ( i -C 3 H 7 ) 2 OH + These data are interpreted in light of a recent radiolysis study, and a thermal cationic chain mechanism for production of ( I -C 3 H 7 ) 2 O consistent with those results is proposed. The value for the proton affinity of SF 6 is also discussed in some detail.