High-resolution FTIR measurement of the line parameters in the fundamental band of HI

The linestrengths and self-broadening coefficients are determined from high-resolution measurements for P(1)-P(10) and R(0)-R(15) lines in the fundamental vibration-rotation band of hydrogen iodide at different gas pressures in the range of 2-280 Torr. Dipole matrix elements are calculated from the linestrength data. New values of the Herman-Wallis coefficients obtained, C₁₀=0.1319, D₁₀=4.41×10^-3, are in a better agreement with theory than previously reported. A significant influence of the hyperfine splitting on the spectral line profiles is demonstrated.     

Spectral line parameters in the (2 ← 0) overtone band and the dipole moment function of the HI molecule

We present here new high-resolution experimental data on the linestrengths and pressure-broadened Lorentzian widths for the P₂(13) to R₂(12) vibration-rotation lines in the first overtone absorption band of hydrogen iodide. By combining the measured linestrengths with our previous results for the fundamental band [J. Mol. Spectrosc. 218 (2003) 75] and with other published data for the higher-overtone bands of this molecule, an improved dipole moment expansion as a function of the dimensionless reduced nuclear displacement x is obtained: μ(x)=0.4471(5)−0.0772(2)x+0.542(3)x²−1.90(2)x³. This experimental dipole moment function is compared with the results of a few recent non-relativistic and relativistic ab initio calculations. The agreement between theoretical and experimental Herman-Wallis coefficients for the first two vibrational bands of HI is found best as ever reported before.     

Self-broadening and shifting of HI lines in the 1-0 and 2-0 infrared bands

Pressure-broadening and -shifting coefficients of pure HI at room temperature have been determined from fits of high-resolution Fourier transform spectra in the fundamental and first overtone infrared bands. The results indicate that the measured widths are almost identical in both bands and decrease significantly with the rotational quantum number. On the contrary, the pressure-induced shifts show a strong dependence on both the rotational and vibrational states. These results are compared with predictions of a semi-classical model. The latter leads to calculated values in good agreement with measurements and shows that the broadening is dominated by electrostatic interactions due to the (permanent) electric dipole and quadrupole moments. On the contrary, the observed shifts cannot be explained without the introduction of a significant vibrationally dependent isotropic potential. The effects of line coupling between hyperfine components are also discussed although they are expected to be small and cannot be observed from the measured spectra. Finally, some tabulated values of calculated widths and shifts vs. quantum numbers and temperature are proposed. They should be useful for infrared sounding of HI amounts, particularly in the monitoring of the hydrogen production through the sulfur-iodine thermochemical cycle.     

Rearrangement of Derivatives of 1,3-Dithian-5-amineinto Bicyclic 2-Thiazolidines. Crystal Structures of cis- and trans-1-(2-Aryl-1,3-dithain-5-yl)-2-thioureas and cis- and trans-5-Aryl-3-imino-7,7a-dihydro-1H,3H,5H-thiazolo[3,4-c]thiazoles

Under conditions normally applied to transform thioureas into the corresponding carbodiimides, cis- and trans-1-(2-aryl-1,3-dithian-5-yl)-2-thioureas 7 and 8 undergo a rearrangement to 5-aryl-3-imino-7,7a-dihydro-1H, 3H, 5H-thiazolo[3,4-c]thiazoles 9/10 with cis- and trans-fused rings, respectively. The structures of these novel heterocycles were established by X-ray analysis of compounds 9a , 9d , and 10d . The cis-fused compounds 9 are the thermodynamically more stable ones. The stereochemical outcome of the rearrangement depends on the carbenium ion stabilizing capability of the aryl moiety and on the reagent system applied. With Ar = Ph, p-Cl-Ph, p-O₂N-Ph, the reaction can be directed to deliver mainly either the cis-thiazolothiazoles 9 or the trans-thiazolothiazoles 10 . With Ar = 5-methyl-4-imidazolyl or p-Me₂N-Ph, formation of the cis-thiazolothiazoles ( 9a and 9b , resp.) is strongly favored independently of the reaction conditions, In contrast to it 2-aryl analogs, (1,3-dithian-5-yl)-2-thiourea 7g can be transformed into the carbodiimide 11 . Under rigorous conditions, 11 also undergoes rearrangement to the corresponding thiazolothiazole 9g . Mechanisms explaining the above findings are discussed. Reaction of trans-2-phenyl-1,3-dithian-5-amine 6d with phosgene or trichloromethyl chloroformate gives the 5-phenyl-7,7a-dihydro-1H,3H,5H-thiazolo[3,4-c]-thiazol-3-ones 12 and 13 , whereas the amine 5g lacking an aryl substitutent forms the sable isocyanate 14 . Compound 14 is transformed into the corresponding thiazolothiazolone 15 by refluxing in diglyme. Syntheses are described for the 1,3-dithian-5-amines 5 / 6 and the thioureas 7 / 8 derived therefrom. The relative configuration of 7d and 8d was determined by X-ray analysis. NMR data then allowed to assign the configurations of all compounds of types 7 and 8 .     

The crystal structure of the L1 intermediate of halorhodopsin at 1.9 angstroms resolution

The mutant T203V of the light driven chloride pump halorhodopsin from Halobacterium salinarum was crystallized and the X-ray structure was solved at 1.6 angstroms resolution. The T203V structure turned out to be nearly identical to the wild type protein with a root mean square deviation of 0.43 angstroms for the carbon alpha atoms of the protein backbone. Two chloride binding (CB) sites were demonstrated by a substitution of chloride with bromide and an analysis of anomalous difference Fourier maps. The CB1 site was found at the same position as in the wild type structure. In addition, a second chloride binding site CB2 was identified around Q105 due to higher resolution in the mutant crystal. As T203V showed a 10 times slower decay of its photocycle intermediate L, this intermediate could be trapped with an occupancy of 60% upon illumination at room temperature and subsequent cooling to 120 degrees K. Fourier transform infrared spectroscopy clearly identified the crystal to be trapped in the L1 intermediate state and the X-ray structure was solved to 1.9 angstroms resolution. In this intermediate, the chloride moved by 0.3 angstroms within binding site CB1 as indicated by peaks in difference Fourier density maps. The chloride in the second binding site CB2 remained unchanged. Thus, intraproteinous chloride translocation from the extracellular to the cytoplasmic part of the protein must occur in reaction steps following the L1 intermediate in the catalytic cycle of halorhodopsin.     

Strategies for isotope ratio measurements with a double focusing sector field ICP-MS

A single collector double focusing sector field ICP-MS is evaluated for the determination of isotope ratios. Spectral interferences (e.g. ⁴⁰Ar²³Na on ⁶³Cu) can lead to calculation of inaccurate ratios. The use of high resolution enables such interferences to be separated from the isotopes of interest. External reproducibilities of < 0.02% are shown for uninterfered isotopes (measured at low resolution R = 300) and < 0.1% for interfered isotopes which required the use of medium (R = 4000) and high resolution (R = 10000). Received: 11 January 1999 / Revised: 8 April 1999 / Accepted: 11 April 1999     

Disproportionation of thermoelectric bismuth telluride nanowires as a result of the annealing process

P-type thermoelectric bismuth telluride nanowires were fabricated by pulsed electrodeposition in anodic aluminium oxide (AAO) membranes. Subsequently, the nanowires were annealed at 423, 523 and 673 K in an inert atmosphere for 4 h. With increasing temperature, it was observed that the Te compound incongruently sublimates due to its high vapor pressure, leading to disproportionation (from Bi(2)Te(3) to Bi(4)Te(3)via Bi(4)Te(5)). The crystalline structure of the nanowires was then investigated using XRD and SAED, with nanowire compositions investigated using an EDX attached to a TEM. The crystallinity of the nanowires was found to be enhanced with increased annealing temperature, and nanowires annealed at 673 K were stably maintained in the Bi(4)Te(3) phase. Additionally, the Seebeck coefficient was determined and the thermopower of nanowires annealed at a temperature of 423 K was shown to be slightly enhanced. Significantly suppressed Seebeck values for annealing temperatures of 523 K and 673 K were also observed.