Far-Infrared Fourier Spectroscopy as a Method for Structure Determination in Chemistry

Couched in the often confusing term “Fourier Spectroscopy” is the combined exploitation of a fundamental physical concept, a simple mathematical principle, and use of modern data technology. Introduction of this relatively young method into instrument technology has given great impetus to nuclear magnetic resonance and infrared spectroscopy. The infrared spectroscopic investigation of low frequency molecular vibrations has especially profited; in this connection one speaks of far infrared (FIR) Fourier Spectroscopy, which has opened up numerous interesting applications in organic, inorganic, and physical chemistry.     

Mössbauer,far-infrared and Raman spectra of tetrachloro[1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadiene] tin(IV)

Summary The dependence of the logarithm of the area under the tin-119 Mössbauer resonance (A at different temperatures are normalized toA ₇₇) vs. temperature is measured for tetrachloro[1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadiene] tin(IV). The slope of the plot of lnA vs.T is –2.46·10^–2K^–1, suggesting a monomeric structure. In the vibrational spectra the significant stretching vibrations agree with acis octahedral configuration of C_2v symmetry.

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Mössbauer-, Fernes-Infrarot- und Raman-Spektren von Tetrachlor[1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadien]zinn(IV)

Zusammenfassung Die Abhängigkeit des Logarithmus der Fläche unter der Zinn-119-Mössbauer-Resonanz (A in verschiedenen Temperaturen werden zuA ₇₇ normalisiert) von der Temperatur wurde für Tetrachlor[1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadien]zinn(IV) gemessen. Der Anstieg lnA gegenT von –2.46·10^–2K^–1 spricht für eine monomere Struktur. In den Vibrations-Spektren stimmen die wichtigsten Dehnungsschwingungen mit einercis-oktaedrischen Konfiguration von C_2v-Symmetrie überein.

     

[M(Im)2X2]型配合物的Far-IR和Raman光谱的理论研究

本文用从头计算RHF和密度泛函B3LYP方法以及LanL2DZ，SDD和6-31G(d)基组计算了配合物M(Im)₂X₂ (Im=imidazole；M=Zn(Ⅱ)，Pd(Ⅱ)，Pt(Ⅱ)；X=F，Cl，Br，I)的几何构型以及Far-IR和Raman振动频率。计算结果表明，对Zn(Ⅱ)配合物而言,B3LYP/6-31G(d)方法得到的几何参数与实验值吻合得最好，B3LYP/SDD次之。在计算Far-IR和Raman振动频率时，发现采用6-31G(d)基组，两种方法计算的结果差别不大。对LanL2DZ和SDD基组而言，对计算结果影响较大的是理论方法，基组影响甚微，个别的振动频率基组影响较大，相比较而言，SDD基组得到的结果更好一些。本文所使用的两种计算方法都能得到与实验值比较吻合的结果，而用从头计算RHF方法计算的结果与实验值更接近一些。在此基础上，预测了Pd(Ⅱ)和Pt(Ⅱ)配合物的Far-IR和Raman振动频率。     

Some sum-rule considerations relative to optical absorption in tetrahedrally bonded amorphous semiconductors for the low-frequency region of the far-infrared range

Within the context of large clusters in tetrahedrally bonded amorphous semiconductors, asymptotic behaviour of the integrated optical absorption for the low margin of the far-infrared region is examined theoretically starting from considerations relative to electronic density of states.     

Frequency measurement of pure rotational transitions of OD

Frequencies of pure rotational transitions of OD⁻ have been measured in the 1-5 THz region using a high-precision tunable far-infrared spectrometer based on difference frequency of two CO₂ lasers. The measured frequencies were analyzed together with the data in the infrared and the sub-millimeter region to refine the rotational parameters. Isotopically invariant Dunham parameters were also obtained.     

尼龙1010的远红外光谱研究

本文研究了结晶程度不同的尼龙1010远红外光谱的差异,对其谱带进行了经验归属。用分峰方法详细地研究了尼龙1010结晶程度的变化对其远红外谱带的位置、宽度和强度的影响。并对由不同退火方式得到的结晶样品的远红外光谱作了比较,由此证明了两者的结晶结构有所差异。     

Rotational levels of the (0 0 0) and (0 1 0) states of D2O from hot emission spectra in the 320-860 cm region

The far-infrared emission spectra of deuterated water vapour were measured at different temperatures (1370, 1520, and 1950 K) in the range 320-860 cm⁻¹ at a resolution of 0.0055 cm⁻¹. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. More than 1150 new measured lines for the D₂¹⁶O molecule corresponding to transitions between highly excited rotational levels of the (0 0 0) and (0 1 0) vibrational states are reported. These new lines correspond to rotational states with higher values of the rotational quantum numbers compared to previously published determinations: J_max=26 and for the (0 0 0) ← (0 0 0) band, J_max=25 and for the (0 1 0) ← (0 1 0) band, and J_max=26 and for the (0 1 0) ← (0 0 0) band. The estimated accuracy of the measured line positions is 0.0005 cm⁻¹. To our knowledge no experimentally measured rotational transitions for D₂¹⁶O within an excited vibrational state have been available in the literature so far. An extended set of experimental rotational energy levels for (0 0 0) and (0 1 0) vibration states including all previously available data has been determined. For the data reduction we used the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.0012 cm⁻¹ for 692 rotational levels of the (0 0 0) state and 0.0010 cm⁻¹ for 639 rotational levels of the (0 1 0) vibrational state. A comparison of the observed energy levels with the best available values from the literature and with the global predictions from molecular electronic potential energy surface [J. Chem. Phys. 106 (1997) 4618] for the (0 0 0) and (0 1 0) states is discussed.     

Predicted new optically pumped FIR molecular lasers

A total of nine cw FIR laser lines are reported from two new FIR laser molecules; CH₂CHF and S¹⁸O₂. These two are from a list of twelve candidate molecules that were predicted using a set of selection criteria. The candidate D₂ ¹⁸O was tested, but did not lase. Combining these results with independent studies on other candidates, brings the number of proven laser molecules to 4 out of 5 that were tested. These results confirm the value of the selection criteria as a guideline for predicting new optically pumped FIR laser molecules.Work supported by the Department of Energy     

The ring-puckering potential energy function and theoretical calculations for silacyclopent-2-ene-d0 and 1,1-d2 and the difluoro and dichloro derivatives

High level ab initio and DFT calculations have been carried out for silacyclopent-2-ene and its 1,1-d₂, 1,1-difluoro, and 1,1-dichloro derivatives. The previously published far-infrared spectra of the ring-puckering vibration, which had been interpreted to be characteristic of a rigid planar molecule, have been reanalyzed for the hydride and 1,1-d₂ derivative. Both the spectra and the theoretical calculations show the molecule to have a small barrier to planarity. The experimental data analyzed with a Gaussian barrier produce a barrier of 49 cm⁻¹ as compared to a value of 47 cm⁻¹ computed using the CCSD/6-311++G(d,p) basis set. The experimental value for the deuteride was determined to be 41 cm⁻¹ from the one-dimensional approximation. All MP2 and DFT computations for the 1,1-difluoro derivative predict a planar structure whereas the MP2 computation when used with triple-ζ basis set predicts a barrier of 13 cm⁻¹ for the chloride. Vibrational frequencies were also computed for these molecules and compared to experimental results for the characteristic frequencies for these types of molecules.     

Estimation of the solitary-wave energy content in solid dielectric media with optical strong nonlinearity in the far-infrared range

The energy content of temporal solitary far-infrared waves propagating in solid dielectric media according to the optical lossless cubic-quintic Schrödinger equation is estimated analytically. In fact the above energy content, which is one of the two fundamental invariant quantities associated with the equation in question, is found to be an affine function of a key nonlinearity parameter.