New analytical bending and stretching, ground electronic state, potential energy surfaces for CH(3)F are reported. The surfaces are expressed in bond-length, bond-angle internal coordinates. The four-dimensional stretching surface is an accurate, least squares fit to over 2000 symmetrically unique ab initio points calculated at the CCSD(T) level. Similarly, the five-dimensional bending surface is a fit to over 1200 symmetrically unique ab initio points. This is an important first stage towards a full nine-dimensional potential energy surface for the prototype CH(3)F molecule. Using these surfaces, highly excited stretching and (separately) bending vibrational energy levels of CH(3)F are calculated variationally using a finite basis representation method. The method uses the exact vibrational kinetic energy operator derived for XY(3)Z systems by Manson and Law (preceding paper, Part I, Phys. Chem. Chem. Phys., 2006, 8, DOI: 10.1039/b603106d). We use the full C(3v) symmetry and the computer codes are designed to use an arbitrary potential energy function. Ultimately, these results will be used to design a compact basis for fully coupled stretch-bend calculations of the vibrational energy levels of the CH(3)F system.
Surface-enhanced resonance Raman scattering (SERRS) provides intense Raman signals that are shown here to be stable in a target and to be detectable at least 10 meters from the spectrometer. The results indicate that SERRS labeling of objects and their detection at a distance with a low-power laser is feasible. Rhodamine and a dye specifically designed to give good surface adhesion, [4(5′-azobenzotriazyl)-3,5-dimethoxyphenylamine] (ABT DMOPA), were adsorbed onto silver particles and the particles dispersed in poly(vinyl acetate) (PVA) and varnish. SERRS from rhodamine was not detected from colloid dispersed either in PVA or varnish, presumably due to displacement of the dye from the silver surface. ABT DMOPA gave good SERRS. Maps of the SERRS intensity of films indicated variability of 10–20% if ultrasound was applied to improve dispersion during mixing. Scattering performance was evaluated using a system with the sample held up to one meter from the probe head. The intensity of the scattering from samples kept in the dark showed little change over a period of up to one year. However, when the samples were left in direct sunlight, the scattering intensity dropped significantly over the same period but could still be determined after eight months. An optical system was designed and constructed to detect scattering at longer distances. It consisted of a probe head based on a telephoto or CCTV lens that was fiber-optically coupled to the spectrometer. Effective detection of SERRS was obtained 10 m from the spectrometer using 3.6 mW of power and a 20 s accumulation time.
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