298 

 interpret. Halogenated species are excellent candidates for ECNCI; however, 

 adduct formation (e.g. [M+Cl]") may occur [72,81,107,108,114,118-120]. Ion source 

 surface or wall reactions may take place, ultimately complicating mass spectra 

 [114,119,121]. Tetracyanoethylene (TCNE), having a relatively high (positive) EA, 

 readily undergoes EC reactions. It is also particularly susceptible to unexpected ion 

 formation from electron capture [119,121,122]. This compound, when examined by 

 ECNCI with methane and with carbon dioxide reagent gases revealed the absence 

 of unexpected ions for COj/ECNCI [121]. 



ECNCI with Carbon Dioxide 



Carbon dioxide has been examined previously as a moderator for thermal 

 electron production for ECNCI of TCNE [121]. It has been shown that when mixed 

 with argon for NCI work, it will enhance the production of the [M-H]~ ion [123]. 

 The allure of CO2 to work contained in this dissertation is from the potentially 

 simplistic mass spectra for the determination of volatile skin emanations which can 

 undergo electron capture. 



Carbon dioxide is efficient at relaxing electron energy distributions, i.e. 

 forming thermal electrons [124,125]. The physical reason for this is the ability of the 

 CO2 molecule to form a short-lived ion (COj"), which autodetaches a lower energy 

 electron, leaving CO2 in a vibrationally excited state [126]. By virtue of the size of 

 a CO2 molecule, it is also efficient at collisional quenching (compared to other inert 



