THE DETERMINATION OF COLLISION CROSS-SECTIONS

Collision cross-sections of ions, sigma(t)0, can be accurately obtained by extrapolating sigma(t), to zero target gas pressure. thus eliminating the error in the collision path length, l(n), caused by target gas leaking out of the collision cell, sigma(t)0 values for various ions have been determined and contain structural information. For normal alkanes (n = 1-10) sigma(t)0 steadily increases from 3.4 to 14.2 angstrom2 by 1.2 angstrom2 per methylene unit. The observation that ions with cyclic structures have smaller total collision cross-sections than corresponding non-cyclic species could be general, as observed for cyclohexane, cyclohexanone and the C2H3O+ ions from oxirane with respect to acetyl cations. The benzene and pyridine dications cannot be considered as pure six-membered ring species since their sigma(t)0 values are significantly larger than those of the singly charged ions.