Ultraviolet-Visible Absorption Spectroscopy of MoCl 5 , MoOCl 4 , and MoO 2 Cl 2 Vapors.

This article reports quantitative absorption spectra for MoCl 5 , MoOCl 4 , and MoO 2 Cl 2 in the vapor phase from 45,500 to 15,500 cm -1 (645 to 220 nm). Spectra are obtained in an ultrahigh purity stainless steel vacuum system by rapidly sampling a range of analyte partial pressures. The short measurement times and the differential absorbance method employed here minimize effects from uncontrolled transients such as window deposits. A detailed analysis of replicate measurements and time-resolved spectra shows generally reproducible spectral response from MoCl 5 vapors at 120 °C. The presence of HCl and MoOCl 4 impurities in the MoCl 5 vapor samples is determined to be unlikely based on the analysis of absorbance-pressure curves and spectral peak fitting. Comparison with MoOCl 4 and MoO 2 Cl 2 spectra shows a unique spectral fingerprint for MoCl 5 at 28,500 cm -1 providing a convenient means of discriminating between MoCl 5 and its oxychlorides in the visible wavelengths. Adsorption behavior of MoCl 5 on surfaces is also discussed with particular emphasis on the use of MoCl 5 as a reactant in vapor phase thin film deposition processes.