Temperature variation of mass spectra of hydrocarbons

The te mpera t ure variation s of the mass spectra of a variety of hydrocarbon s have been mea sured by using a Consoli dated mass spectrometer . M easure ments have been made in t he temperature range of 100 0 to 300 0 C on a number of selected mass p eaks in t he spectra of 21 co mpounds. The sensitivity (curren t per uni t pressure) of t he maximum peak and t he ratio of other peaks to t he maximum p eak have been measured as a func t ion of temperat ure of the ion source. The perce ntage change of sensitivi ty or of pattern p er d egree C at 250 0 C has been defin ed a s t he tem perat ure coefficient. This changes very little with temperature. The te mperature coeffici ents of sensit ivi ty for A a nd N2 are -0 .23 a nd -0.18. Sensit ivity coefficients of the max imum peaks of t he hydrocarbon s ran ge fr om -0.2 to 0 ; and pattern coeffi cien ts of most of t he peaks have small negative or positive val ues, but the molec ul e ion s ha ve large r n egative coe ffi cients up to -1.5 percen t per deg ree. Th ere is an inverse correlat ion between t he s ize of t he molecul e ion peak r elative to t he s um of a ll the peaks and t he te mpera t ure coefficie nts. Spontaneous di ssociation of m olecul e ions because of thermal energy can account for thi s co rrelation between peak heigh t and tcmpera ture coe ffi cien t. Published appearan cc po te n t ial data for a fe w of t hese molec ul es give a basis for co mputing t he stabili ty of t he ion s and show t hat t herm al d issoc iatio n is to be exp ected at 200 0 to 300 0 C .