Negative chemical ionization mass spectrometric studies on dissociative electron attachment processes of chloroethylenes and bromoethylenes

The temperature dependence of the formation of negative ions from chloroeth ylenes (cis-1,2-C2H2Cl2, trans-1, 2-C2H2Cl2, C2HCl3, C2Cl3F, C2Cl4) and bro moethylenes (cis-1,2-C2H2Br2, trans-1,2-C2H2Br2, C2HBr3, 1,1'C2Br2F2) was s tudied using negative chemical ionization mass spectrometry. The halide ion was observed for all samples. Other fragment anions, (M-X)(-) (parent mole cule, M, less one halogen atom, X)(-) and X-2(-) were produced for some sam ples. The former was observed for trans-1,2-C2H2X2 and C2HBr3, and the latt er for 1,2-C2H2Cl2, cis-1,2-C2H2Br3, and C2HBr3 The branching ratio of X-2( -) and (M-X)- decreases with increasing die temperature. The branching rati o of X-2(-) is considerably different for chloroethylenes and for bromoethy lenes.