J. Phys. Chem. A 2009, 113, 5119–5127
5119
Cryogenic Terahertz Spectrum of (+)-Methamphetamine Hydrochloride and Assignment Using Solid-State Density Functional Theory Patrick M. Hakey,† Damian G. Allis,†,‡ Wayne Ouellette,† and Timothy M. Korter*,† Department of Chemistry, Syracuse UniVersity, Syracuse, New York 13244-4100, and Nanorex, Inc., P.O. Box 7188, Bloomfield Hills, Michigan 48302-7188 ReceiVed: NoVember 21, 2008; ReVised Manuscript ReceiVed: March 2, 2009
The cryogenic terahertz spectrum of (+)-methamphetamine hydrochloride from 10.0 to 100.0 cm-1 is presented, as is the complete structural analysis and vibrational assignment of the compound using solid-state density functional theory. This cryogenic investigation reveals multiple spectral features that were not previously reported in room-temperature terahertz studies of the title compound. Modeling of the compound employed eight density functionals utilizing both solid-state and isolated-molecule methods. The results clearly indicate the necessity of solid-state simulations for the accurate assignment of solid-state THz spectra. Assignment of the observed spectral features to specific atomic motions is based on the BP density functional, which provided the best-fit solid-state simulation of the experimental spectrum. The seven experimental spectral features are the result of thirteen infrared-active vibrational modes predicted at a BP/DNP level of theory with more than 90% of the total spectral intensity associated with external crystal vibrations. I. Introduction Terahertz (THz, far-infrared,
