The salt 1,1,3,3-tetramethylguanidinium bromide, [((CH(3))(2)N)(2)C═NH(2)](+)Br(-) or [tmgH]Br, was found to melt at 135(5) °C, forming what may be referred to as a moderate temperature ionic liquid. The chemistry was studied and compared with the corresponding chloride compound. We present X-ray diffraction and Raman evidence to show that also the bromide salt contains dimeric ion pair "molecules" in the crystalline state and probably also in the liquid state. The structure of [tmgH]Br determined at 120(2) K was found to be monoclinic, space group P2(1)/n, with a = 7.2072(14), b = 13.335(3), c = 9.378(2) Å, β =104.31(3)°, Z = 2, based on 11769 reflections, measured from θ = 2.71-28.00° on a small colorless needle crystal. Raman and IR spectra are presented and assigned. When heated, both the chloride and the bromide salts form vapor phases. The Raman spectra of the vapors are surprisingly alike, showing, for example, a characteristic strong band at 2229 cm(-1). This band was interpreted by some of us to show that the [tmgH]Cl gas phase should consist of monomeric ion pair "molecules" held together by a single N-H(+)···Cl(-) hydrogen bond, the stretching vibration of which should be causing the band, based on ab initio molecular orbital density functional theory type calculations. It is not likely that both the bromide and chloride should have identical spectra. As explanation, the formation of 1,1-dimethylcyanamide gas is proposed, by decomposition of [tmgH]X leaving dimethylammonium halogenide (X = Cl, Br). The Raman spectra of all gas phases were quite identical and fitted the calculated spectrum of dimethylcyanamide. It is concluded that monomeric ion pair "molecules" held together by single N-H(+)···X(-) hydrogen bonds probably do not exist in the vapor phase over the solids at about 200-230 °C.

Abstract:Two fiber Raman probes are presented, one based on an optically-poled double-clad fiber and the second based on an opticallypoled double-clad fiber coupler respectively. Optical poling of the core of the fiber allows for the generation of enough 532nm light to perform Raman spectroscopy of a sample of dimethyl sulfoxide (DMSO), when illuminating the waveguide with 1064nm laser light. The Raman signal is collected in the inner cladding, from which it is retrieved with either a bulk dichroic mirror or a double-clad fiber coupler. The coupler allows for a substantial reduction of the fiber spectral background signal conveyed to the spectrometer. References and links1. R. L. McCreery, M. Fleischmann, and P. Hendra, "Fiber optic probe for remote Raman spectrometry," Anal.Chem. 55 (1), 146-148 (1983). 2. I. Lewis and P. Griffiths, "Raman spectrometry with fiber-optic sampling," Appl. Spectrosc. 50, 12A-30A (1996). 3. T. Cooney, H. Skinner, and S. Angel, "Comparative study of some fiber-optic remote Raman probe designs. Part I: Model for liquids and transparent solids," Appl. Spectrosc. 50, 836-848 (1996). 4. T. Cooney, H. Skinner, and S. Angel, "Comparative study of some fiber-optic remote Raman probe designs. Part II: Tests of single-fiber, lensed, and flat-and bevel-tip multi-fiber probes," Appl. Spectrosc. 50, 849-860 (1996). 5. U. Utzinger and R. R. Richards-Kortum, "Fiber optic probes for biomedical optical spectroscopy," J. Biomed.Opt. 8, 121-147 (2003). 6. M.J. Pelletier, "Fiber optic probe with integral optical filtering," USA Patent no. 5862273 (1999). 7. A. C. Brunetti, L. Scolari, T. Lund-Hansen, J. Weirich, and K. Rottwitt, "All-in-fiber Rayleigh-rejection filter for Raman spectroscopy," Electron. Lett. 48(5), 275-276 (2012). 8. B. Redding and H. Cao, "Using a multimode fiber as a high-resolution, low-loss spectrometer," Opt. Lett. 37(16), 3384-3386 (2012). 9. V. Pruneri, G. Bonfrate, P. G. Kazansky, D. J, Richardson, N. G. Broderick, J. P. de Sandro, C. Simonneau, P.Vidakovic, and J. A. Levenson, "Greater than 20%-efficient frequency-doubling of 1532-nm nanosecond pulses in quasi-phase matched germanosilicate optical fibers," Opt. Lett. 24, 208-210 (1999 1911-1913 (2006). 20. M. Buric, K. Chen, J. Falk, and S. Woodruff, "Enhanced spontaneous Raman scattering and gas composition analysis using a photonic crystal fiber," Appl. Opt. 47, 4255-4261 (2008).

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