Vibrational spectrum of methoxytrimethylsilane M. Montejo a , F. Partal Uren ˜a a, * , F. Ma ´rquez a , I.S. Ignatyev b , J.J. Lo ´pez Gonza ´lez a a Department of Physical and Analytical Chemistry, Experimental Sciences Faculty, University of Jae ´n, Campus ‘Las Lagunillas’, 23071 Jae ´n, Spain b Radiochemistry Laboratory, Department of Chemistry, St Petersburg State University, St Petersburg 199034, Russian Federation Received 24 November 2004; revised 23 December 2004; accepted 24 December 2004 Available online 11 February 2005 Abstract Gas and liquid phase infrared spectra and the liquid phase Raman spectrum of methoxytrimethylsilane (MTMS) have been newly recorded. Theoretical calculations at the B3LYP level, using two different basis sets, i.e. the standard 6-31G* and the Huzinaga–Dunning type DZPCdiff, together with the application of SQMFF methodology have been used for the revision of the vibrational spectra of the title molecule, reproducing the whole IR and Raman spectral profiles. This has allowed us to propose the reassignment of some fundamental bands of its vibrational spectra, namely n 27 , n 35 , n 42 , n 45 , n 46 and n 48 and to compare them with those of previous assignments. The scale factors obtained for the trimethylsilyl group of this molecule along with those obtained by our group for a set of trimethylsylil derivatives will be used to get a specific set of averaged values suitable for the prediction of vibrational spectra of less stable species containing the Me 3 SiO group. q 2005 Elsevier B.V. All rights reserved. Keywords: Methoxytrimethylsilane; Vibrational spectra; IR; Raman 1. Introduction It is well-known that mono-, di- and trialkyl-substituted silanols are usually involved in sol–gel processes for manufacturing glasses, ceramics, films, etc. [1]. Vibrational spectroscopy appears to be suitable for monitoring these reactions [2]. However, a deep knowledge of the vibrational spectra of the above mentioned silanols is necessary for this purpose. Unfortunately, spectroscopic experimental data of silanols are usually hard to obtain because of their high reactivity. In addition, the Si–O stretching and the Si–O–H deformation normal modes (which are very useful in the analysis of the progress of the reactions of hydrolysis and condensation in sol–gel processes) are located in the same spectral region, where skeletal normal modes appear. These problems can be solved with the study of related less reactive species than silanols or trialkylhalides, with the aim of reaching a description as complete as possible of the trialkylsilyl group. Thus, with the support of the SQMFF [3] methodology, our goal is to get a set of specific and averaged scale factors for the trimethylsilyl group in this sort of molecules. This could be later transferred to larger molecules which take part in those highly reactive real systems. For this task, we have revised elsewhere [4,5] the analysis and the assignment of the vibrational spectra of trimethylsilane, fluorotrimethylsilane, chlorotrimethylsilane and bromotrimethylsilane. Likewise, DFT theoretical calcu- lations and SQMFF procedure were employed in Refs. [4,5] for analysing their structure and vibrational spectra. Studies on the vibrational assignment of the title molecule are available in the literature. Forneris et al. [6] assigned the vibrational spectrum using data from the IR of the gas. Some years later Marchand et al. [7] discussed the assignment of some normal modes in several related alkoxysilanes (including methoxytrimetilsilane), silanes, siloxanes and ethers, using data from IR and Raman spectra. In 1977, Tenisheva et al. [8] recorded the IR and Raman spectra in different phases of MTMS and its completely and partially deuterated derivatives, and performed normal coordinates calculations in order to assign the whole vibrational spectra. Durig et al. [9] made, to the best of our knowledge, the last revision of the assignment based on newly obtained IR and Raman spectra 0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2004.12.040 Journal of Molecular Structure 744–747 (2005) 331–338 www.elsevier.com/locate/molstruc * Corresponding author. Tel.: C34 953 212555; fax: C34 953 212141. E-mail address: fpartal@ujaen.es (F. Partal Uren ˜a).