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The Infrared Spectrum of a Molecular Aggregate. The HCN Dimer Isolated in an Argon Matrix J. Pacansky IBM Research Laboratory, San Jose, California 95 193 (Received June 9, 1977) Publlcation costs assisted by
IBM Research laboratory
Spectral properties of well-defined molecular aggregates are difficult to obtain. A study is presented which demonstrates that a well-defined molecular aggregate may be produced by photochemical methods. This is specifically shown by producing the HCN dimer from the photochemical decomposition of s-tetrazine. The infrared spectrum of the dimer clearly shows that the vibrational bands associated with the hydrogen bond are intensified and broadened in comparison to those not involved in the hydrogen bond.
Introduction The matrix isolation technique has amply demonstrated that spectroscopic properties of isolated molecules may be readily 0btained.l Here, and in subsequent studies, we show that spectroscopic properties of well-defined aggregates of molecules may also be observed utilizing the matrix isolation technique. This is demonstrated by showing the infrared spectrum of the matrix isolated HCN dimer. The unique feature of this spectrum and the manner in which the dimer was formed is that all of the sites in the matrix are occupied by only dimers. The spectra thus clearly reveal the spectroscopic changes which are manifestations of the rather strong hydrogen bond2 (AH= 3.8 kcal/mol) in the dimer. The method used to produce molecular aggregates consist of selecting a system that upon exposure to light photochemically decomposes to the particular aggregate desired. For example, tetrazine3i4has been studied in both the gas and solid phase and appears to quantitatively decompose when exposed to light with wavelength h
