(45a) Decomposition Kinetics of Dimethylcadmium by in-Situ Raman Spectroscopy and Quantum Chemical Calculations

The gas-phase decomposition of dimethylcadmium (Cd(CH3)2), a common precursor for deposition of Cd-VI compounds, was studied. First principles quantum calculations were first performed to better understand the bond dissociation behavior of Cd(CH3)2 and intermediates. DFT calculations (B3LYP) with a conjugated basis set of SDD for Cd, 3-21G for H, and STO-3G for C, was used to estimate the vibrational frequencies for Raman active modes and scattering cross-sections, as well as thermodynamic properties. These basis sets could reproduce previously reported bond dissociation energies and frequencies. The calculations suggest the existence of dimmer formation from two CdCH3 radicals and its frequency was calculated to support the experimental work.

Gas-phase Raman scattering experiments were carried out in an inverted impinging-jet reactor. The measured temperature gradient and concentration profiles were used to estimate kinetic parameters using a validated FEM simulation of the reactor. This analysis indicates dimerization is a higher rate pathway for CdCH3 disappearance than homolytic fission of the final Cd-C bond. Based on experimental measurements, the most likely reaction parameters including rate constant, diffusivity and Raman cross section were estimated.