Experimental Raman spectra of dilute and laser-light-sensitive [Rh4(CO)9(µ-CO)3] and [(µ4-η2-3-hexyne)Rh4(CO)8(µ-CO)2]. Comparison with theoretically predicted spectra

An experimental investigation of n-hexane at high temperature and pressure

At present, no high temperature experiments on phase change are reported. In this study, we have measured the Raman bands ν_s(CH₃), ν_s(CH₂), ν_as(CH₃), and ν_as(CH₂) of n-hexane in a hydrothermal diamond cell up to 588 K. We determined that the liquid-solid phase transition pressure of n-hexane is 1.17 GPa, and we also gave a number of high temperatures and pressures data on phase change which are not reported previously. In addition, we defined the solidus of n-hexane which can be represented by the equation P = 8.581T-1550.16, and the relation dP/dT = 8.581 which can be used to calculate the thermodynamic parameters for n-hexane in the liquid-solid phase transition. For all we know, the above two equations are presented here for the first time. Furthermore, it is the first report here in a graphic way on high-temperature phase change in n-hexane, and it is also the first to be shown in the 3-D figure.

An advanced digital filter for one-dimensional spectroscopic data: minimizing distortion in band shapes and band intensities

A wide variety of digital filters exist for processing one-dimensional (1D) signals; however, the application of some filters results in pronounced systematic distortions in band shapes and band intensities. In the present contribution, filtering is achieved by optimization in which a general objective function is constructed that possesses a number of desirable qualities, such as (1) smoothness of the resulting spectrum as well as (2) statistical constraints on the residual. Since the residual is explicitly used in the optimization, one can control systematic distortions and therefore avoid over-filtering. In tests using a variety of synthetic as well as real 1D spectroscopic data, the filter adequately preserves both band shapes and band intensities. In addition, the filter appears to accommodate homoscedastic, heteroscedastic, and frequency-dependent noise. Examples of its application and usefulness to powder X-ray diffraction (PXRD), Raman, and Fourier transform infrared (FT-IR) emission data are provided. Tests with synthetic data indicate that considerable noise reduction can be achieved in many applications. Finally, an iterative form of the filter is presented. This iterative form further minimizes distortions in band shapes and band intensities when very high levels of denoising are desired. The present filtering approach is an alternative to existing filters, particular when the quality of the residual is important to the user.

Combination of Raman microscopy, multiwell plate experimental designs, and BTEM analysis for high-throughput experimentation

Both nonreactive and reactive multiwell plate experiments were combined with Raman microscopy and band-target entropy minimization (BTEM) analysis. The multicomponent nonreactive experiments showed that accurate pure component spectral estimation is possible without recourse to any spectral libraries. The multicomponent reactive experiments showed that, in addition to accurate pure component spectral estimation, concentration profiles can be obtained for quantitative purposes. In the present case, the solvent and time dependence of a cycloaddition reaction was addressed as the high-throughput experimentation issue. A total of 1152 experimental spectra were collected and analyzed. Two methods were used, namely, (A) each solvent set was individually analyzed and (B) the entire set of spectra, from 4 different solvents, were analyzed all together. Method B provided very satisfactory results. The present study with combined Raman-multiwell plate-BTEM analysis establishes proof of concept. The new approach appears to be applicable to other frequently conducted combinatorial/high-throughput experimentations. These include, but are not restricted to, chemo- and regioselective studies, solid-phase syntheses, etc.