Zero-Pressure Thermal-Radiation-Induced Dissociation of Tetraethylsilane Cation

Abstract

Zero-pressure thermal-radiation-induced dissociation (ZTRID) of tetraethylsilane cation is reported. Dissociation of weakly bound gas-phase cluster ions by the blackbody background radiation field has been shown previously to proceed at an observable rate; the present results represent the first characterization of this process for a covalently bound molecular ion. Thermal-radiation-induced dissociation of the ions was studied at the low-pressure limit in a FT-ICR mass spectromer, and cleavage of the ethyl group from silicon was observed on a time scale of seconds, with the rate being strongly temperature dependent. The activation energy for the loss of one ethyl radical from tetraethylsilane cation was derived from the slope of the Arrhenius plot in the 340−400 K temperature range to be 0.43 ± 0.07 eV. The bond energy (0 K) was determined to be 0.70 ± 0.07 eV using thermal dissociation theory and 0.71 ± 0.07 eV using master-equation modeling. A bond energy of 0.78 eV was assigned at 298 K, and a heat of formation (298 K) of 131.7 kcal mol-1 was derived for the triethylsilyl cation.