THRESHOLD COLLISIONAL ACTIVATION OF FEC2H6+ - FE+.ETHANE VS FE+.DIMETHYL STRUCTURES

Threshold collisional activation (TCA) of FeC2H6+ is studied in a guided-ion beam mass spectrometer. Parent ions are formed by reaction of Fe+ with either ethane or acetone in a flow tube ion source which ensures their thermalization. We present evidence that ions formed in the two ways have different structures corresponding to Fe+-ethane and Fe+-dimethyl, respectively. We determine D-degrees-0(Fe+-C2H6) = 15.3 +/- 1.4 kcal/mol and D-degrees-0(CH3Fe+-CH3) = 43.1 +/- 2.6 kcal/mol and that Fe(C2H6)+ is more stable than Fe(CH3)2+ by 3.5 +/- 1.7 kcal/mol. These experimental values are compared with those from a recent theoretical calculation. The utility of TCA as a proble of thermochemistry and the structure of transition metal-alkane and -dialkyl species is assessed.