Yining Huang

Infrared Study of the Effect of High External Pressures on Crystalline α-Silicon Nitride:

Crystalline silicon nitride (Si3N4) is of considerable interest commercially, e.g., as a passivating layer in the microelectronics industry and in the construction of advanced heat engines. The high-temperature, nitriding processes normally used in the manufacture of this ceramic yield materials in which the ratio of the α- and β-Si3N4 polymorphic, crystalline modifications varies considerably depending on the actual synthetic conditions employed. Almost ten years ago, Luongo showed that IR spectroscopy could readily be used for the rapid, quantitative identification of crystalline α- and β-Si3N4 in the presence of each other, despite the very close structural similarities between the two polymorphic phases. The IR method was based on determining the ratio of the absorbances (I685/I578) of two characteristic marker bands which appear at 685 (α-Si3N4) and 578 cm−1 (β-Si3N4). A graph for determining the relative amounts of the two polymorphic phases in the presence of each other in an unknown sample was published as part of Luongos paper.

High-Pressure Micro-Raman Spectra of Potassium Chromate(VI) and Potassium Tungstate(VI)

The effects of high external pressures on the micro-Raman spectra of potassium chromate, K2CrO4, and potassium tungstate, K2WO4, have been investigated for pressures approaching 45 kbar. There is no evidence for a pressure-induced phase transition in the chromate, but there is clearly such a transition at ∼13 kbar in the tungstate. The pressure sensitivities of the principal bands observed in the spectra of the two salts have been determined. The values obtained are comparable to those reported for simple spinels and somewhat larger than those for scheelites.

Pressure-tuning infrared spectra of the thiamine enzyme ‘active aldehyde’ intermediate 2-(α-hydroxycyclohexylmethyl)thiamine chloride (HCMT · HCl) and its complex with zinc(II), Zn(HCMT)Cl3

Abstract IR spectra of the protonated form of 2-(α-hydroxycyclohexymethyl)thiamine chloride (HCMT · HCl) and the zwitterionic zinc(II) complex, Zn(HCMT)Cl3, have been recorded at room temperature and various pressures up to ∼30 kbar. The majority of the peaks are blue shifted (towards higher wavenumbers) with increasing pressure; the v(OH) and v(NH) vibrations are red shifted. As for the closely related 2-(α-hydroxybenzyl)thiamine hydrochloride ligand and its metal complexes, the pyrimidine skeletal ring vibrations are quite pressure-sensitive (dv/dP>0.50 cm−1/kbar). In solution, the pyrimidine and thiazolium rings of the HCMT ligand adopt an S conformation with respect to one another and this conformation is apparently retained in the solid-state, even at very high pressures, suggesting that its stability may be important in the enzymatic action of thiamine in the presence of divalent metal ions.

A pressure-tuning micro-Raman study of crystalline pentacarbonyl(chloro)rhenium(I), Re(CO)5Cl

Abstract Micro-Raman spectra of crystalline pentacarbonyl(chloro)rhenium(I), Re(CO) 5 Cl, have been recorded at various external pressures up to approximately