Sulfur vibrational frequencies

The sulfur-nitrogen bond length in thiazyl salts is about 1.42 A and the vibrational frequency [v(SN] occurs at 1437 cm in [SNJiAsFg]. The [SN]" cation exhibits an " N NMR resonance at ca. 200 ppm and this technique is useful for monitoring reactions of [SN]". ... 

A 9 cm-1 upshift of the tangential mode (G band) vibrational frequency as well as a 90% decrease in intensity was observed by applying 1.0 V between an individual nanotube and a silver reference electrode in a dilute sulfuric acid solution. 

TABLE 19.1 Gibbs free energy (at 298 K and 1 atm reference pressure) for the addition of water molecules to sulfuric acid, from various calculations and experiments. For the quantum chemical results, the use of harmonic or anharmonic vibrational frequencies has been indicated... 

Figure 9 Sulfur isotope dependence of resonance Raman vibrational frequencies for (a) the [Cu(1.5)-Cu(1.5)] mixed-valence Cua site, obtained with 488-nm excitation (b) the [2Cu(l)2Cu(ll)] Cuz site in semireduced N2O reductase, obtained with 568-mn excitation and (c) the dithionite-reduced Cuz site, obtained with 647-mn excitation. S denotes 230-cm" ice mode from frozen solvent. C denotes a band believed to arise from an altered Cua site. (Reprinted with permission from M.L. Alvarez, J. Ai, W.G. Zumft, J. Sanders-Loehr, and D.M. Dooley, J. Am. Chem. Soc., 2001, 123, 476. 2001 American Chemical Society)...

Ammonia Solutions. It has long been suggested that ammonia solutions age quicker than sodium or potassium solutions of sulfite. We have recorded Raman spectra of three year old 1 M ammonium bisulfite solutions in sealed ampules. These contain not only a solid elemental sulfur phase and solid ammonium sulfate phase, but the liquid phase contains also several percent of dithionate, recognizable by the vibration frequencies of 710 cm- and 1206 cm-, with an intensity ratio of l7io/ -l2Q6 = 3.2. A search for other oxyacids yielded traces of thiosulfate... 

The vibrational frequencies are consistent with unbranched, nonplaiiar structures. The fact that the S—S stretching frequency, although weak, occurs in the infrared, excludes a planar, centrosymmetric trans form for disulfides. In the Raman spectra of di- and polysulfides, no lines are found which can be assigned to a coordinate sulfur-sulfur bond such a bond should be characterized by a rather strong line and its absence implies that branching does not occur. 

Episulfonium ions (ESI) are three-membered sulfur-containing cationic species that have been postulated as intermediates in many reactions. Mechanisms of the reaction of l-alkoxy-2-(arylsulfanyl)alkyl halides with different nucleophiles in the presence of a Lewis acid appear to be more complex because of the possibility of forming either ESIs or oxonium ions (IOS) as intermediates (Figure 27). Dudley212 reported equilibrium structures and harmonic vibrational frequencies of two model compounds related to the intermediates of nucleophilic attack on l-alkoxy-2-(arylsulfanyl)alkyl halides... 

In addition to measuring reaction rates on soot surfaces in the Knudsen cell, we have also used FTIR spectroscopy to investigate the changes in the surface functional groups after the soot is exposed to different species. The FTIR spectrum of the original soot sample, and the changes that occur when the soot is exposed to sulfuric acid vapors have been observed. Some of the soot peaks disappear and new peaks near the sulfate vibrational frequencies clearly show that the surface has been chemically modified. 

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