Photochemical Studies by Means of a Field Ion Mass Spectrometer

Abstract

A mass spectrometric investigation was carried out on the direct photolyses of propene, 1-butene, and hydrazine at 1849 A with a field ion source in a flow system. Comparisons were made with Pt tip and wire emitters. It was found that, without illumination, mass spectra obtained with the wire were accompanied by a number of fragment peaks amounting to almost 1%. Since these peaks interfere with those produced photochemically, the tip emitter was used mostly for the photochemical studies although it gave 100 times less current and was less stable. The photochemical products formed at a gas pressure of 10 μ by a low pressure mercury lamp were detected after approximately 10 m sec. The three main peaks observed in the propene photolysis were at masses 27, 28, and 56, indicating the processes: C3H6+hv→C2H3+CH3, C3H6+hv→C2H4+CH2, CH2+C3H6→C4H8. The photolysis of 1-butene gave four main peaks at masses 40, 41, 42, and 70, suggesting steps, C4H8+hv→C3H4+ (H+CH3) or CH4, C4H8+hv→C3H5+CH3, C4H8+hv→C3H6+CH2, CH2+C4H8C5H10. The only peak found with the photolysis of hydrazine was at mass 17, indicating the step, N2H4+hv→NH3+NH. The possibility of forming these products by secondary processes is discussed.