Abstract

This article reports quantitative absorption spectra for MoCl5, MoOCl4, and MoO2Cl2 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 MoCl5 vapors at 120 °C. The presence of HCl and MoOCl4 impurities in the MoCl5 vapor samples is determined to be unlikely based on the analysis of absorbance-pressure curves and spectral peak fitting. Comparison with MoOCl4 and MoO2Cl2 spectra shows a unique spectral fingerprint for MoCl5 at 28,500 cm-1 providing a convenient means of discriminating between MoCl5 and its oxychlorides in the visible wavelengths. Adsorption behavior of MoCl5 on surfaces is also discussed with particular emphasis on the use of MoCl5 as a reactant in vapor phase thin film deposition processes.

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