Mass and collision cross section determination using a low-vacuum mass spectrometer

A simple low-vacuum mass spectrometer (LVMS) operating in the milliTorr pre ssure range was developed. The instrument resolves masses by time-of-flight measurements and employs a high-gain, fast-response detector that can oper ate at these pressures. This instrument allows simultaneous determination o f mass and collision cross sections of the ions with the bath gas. Here we demonstrate the LVMS's abilities to determine total collision cross section s for the collisions of organic ions with three background gases, He, N-2, and SF6. As a demonstration of the system capabilities, the unimolecular in terconversion of photochemically produced C7H7+ to the tropylium ion struct ure is investigated.