In press, available from the Journal of Physical Chemistry A. The INS experiment was carried out using the TOSCA instrument across the pond at the ISIS facility of the Rutherford Appleton Laboratory. The solid-state calculations were performed, as usual, with DMol3 from Accelrys. The paper was presented originally at the 2005 ACS DC meeting, available in the posters page on this site. Another example of theory and vibrational spectroscopy generating a far more complete picture than crystallography alone.
D. G. Allis and B. S. Hudson
Abstract: The inelastic neutron scattering (INS) spectrum of polycrystalline Cs2[B12H12] is assigned through 1200 cm-1 based on aqueous and solid-state Raman/IR measurements and normal mode analyses from solid-state density functional theory. The Cs+ cations are responsible for frequency shifts of the internal cage vibrational modes and Ih cage mode splittings due to the crystal Th site symmetry. These changes to the [B12H12]-2 molecular modes make isolated molecule calculations inadequate for use in complete assignments. Solid-state calculations reveal that 30/40 cm-1 shifts of Tg/Hg molecular modes are responsible for structure in the INS spectrum unobserved by optical methods or in aqueous solutions.
Welcoming 2006 with a bang. Or the molecular foundations for a bang, anyway. In the Journal of Physical Chemistry A (J. Phys. Chem. A 2006, 110, 1951). The experimental results were provided by TeraView, Ltd., solid-state calculations with DMol3 from Accelrys.
D. G. Allis, D. A. Prokhorova, and T. M. Korter
Abstract: The experimental solid-state terahertz (THz) spectrum (3-120 cm-1) of the beta-crystal form of the high explosive octahydro – 1,3,5,7 – tetranitro – 1,3,5,7 – tetrazocine (HMX) has been analyzed using solid-state density functional theory calculations. Various density functionals (both generalized gradient approximation and local density approximation) are compared in terms of their abilities to reproduce the experimentally observed solid-state structure and low-frequency vibrational motions. Good-to-excellent agreement between solid-state theory and experiment can be achieved in the THz region where isolated-molecule calculations fail to reproduce the observed spectral features, demonstrating a clear limitation of using isolated-molecule calculations for the assignment of THz frequency motions in molecular solids. The deficiency of isolated-molecule calculations is traced to modification of the molecular structure in the solid state through crystal packing effects and the formation of weak C-H…O hydrogen bonds.
Sander Olson was kind enough to offer me a chance to speak… er… type my peace in an interview at nanotech.biz. The link to the interview is HERE. I’m the new interviewee in a list that includes such heavy hitters (and friends/collabs) as Robert Freitas, Tihamer Toth-Fejel, Chris Phoenix, and none other than the good Dr. Hall.