Rotational spectra applications

An excitation-wavelength dependence at the longwave edge of the absorption spectrum has been observed not only for spectral displacement but also for other parameters such as lifetime, quantum yield and apparent rotational rate. Applications to the investigation of polymer rigidity and/or free volume, and to the study of biological systems and excited-state reactions have been developed. 

Sakai, H. (1962). A Slit Function Correction and an Application to the Study of the Absorption Lines in the H20 Pure Rotation Spectrum. U. S. Armed Services Technical Information Agency Report AD287897. 

A significant application of microwave spectroscopy is in the determination of barriers to internal rotation of one part of a molecule relative to another. Internal rotation is a vibrational motion, but has effects observable in the pure-rotation spectrum. If the barrier to internal rotation is very high, then the internal torsion is just like any other vibrational mode, and the rotational constants are affected in the usual way Bv = Be —... 

Depending on the quality of data and the method selected, constraints on the parameters to be estimated may be required in order to get a chemically meaningful solution. In the case of multivariate curve resolution (MCR) (see Section 3.2) performed on one 2D NMR spectrum, application of constraints is mandatory. If constraints are not applied, it can be shown that there is an infinity of equally well-fitting solutions and hence the true underlying parameters (spectra, concentrations) cannot be estimated directly. This is known as the rotational ambiguity of two-way low-rank models. 

The principal application of the Kraitchman equations [Eq. (9)1 is for the determination of the atomic coordinates, at, bSi and cs. From a study of the rotational spectrum of the parent and of a species with single isotopic substitution the coordinates of the substituted atom may be determined. These coordinates are referred to as substitution coordinates or rs coordinates. Each new species yields new coordinates, and since all of the coordinates are in the same coordinate system, the calculation of substitution or rs bond distances and bond angles is a simple process. Costain,s demonstrated that there are definite advantages to the use of the Kraitchman equations to obtain molecular parameters. These advantages are sufficient to make the use of Kraitchman s equations the preferred method of structure determination from ground-state rotational constants. 

Microwave spectroscopy is used to measure dipole moments and moments of inertia of simple molecules in the gas phase. The chemical composition of the molecule and the masses of its atoms are usually known, so one uses moments of inertia to help determine the structure of a molecule, perhaps the most important application of microwave spectroscopy. Sometimes it is necessary to use x-ray data also to supplement the microwave data. From the pattern of the rotational spectrum... 

The infrared spectrum, also known as molecule vibration and rotation spectrum, is used in fundamental research of molecular structure and analysis of chemical components, and the latter is the widest application of the infrared spectrum. The structure of an unknown sample can be deduced according to the position and shape of absorption peaks in the spectrum and contents of the components of the mixture can be detected by the strength of the characteristic peaks. Infrared spectrometry has become the most widely used analysis and test instrument because of its analytical characteristics of high efficiency, high sensitivity, lower sample quantity, and good sample applicability. 

An important application of theoretically calculated electric field gradients at the nucleus is in the determination of nuclear quadrupole moments. The interaction between the nuclear quadrupole moments and the electric field gradient at the nucleus can be measured with unprecedented accuracy (compared to other experimental approaches for determining nudear quadrupole moments) in microwave spectroscopy. These interactions give rise to the fine structure in the rotational spectrum of the molecule. Highly accurate estimates for the electric field gradient at the nucleus can often be calculated theoretically (since this is a first-order molecular property). By combining these theoretical results with experimental observations, accurate values of the nuclear quadrupole moments can be obtained, and this approach has been used to revise previously estimated nudear quadrupole moments (see, e.g., KeUo and Sadlej 1998). 

One possibility for this was demonstrated in Chapter 3. If impact theory is still valid in a moderately dense fluid where non-model stochastic perturbation theory has been already found applicable, then evidently the continuation of the theory to liquid densities is justified. This simplest opportunity of unified description of nitrogen isotropic Q-branch from rarefied gas to liquid is validated due to the small enough frequency scale of rotation-vibration interaction. The frequency scales corresponding to IR and anisotropic Raman spectra are much larger. So the common applicability region for perturbation and impact theories hardly exists. The analysis of numerous experimental data proves that in simple (non-associated) systems there are three different scenarios of linear rotator spectral transformation. The IR spectrum in rarefied gas is a P-R doublet with either resolved or unresolved rotational structure. In the process of condensation the following may happen. 

Figure 3 demonstrates the simplifications in the spectrum of an optimized laser pulse that can be achieved through the application of the sifting technique [see Fq. (7)]. The excitation efficiency of the pulse is only minimally reduced due to the additional restrictions imposed in the sifting procedure. The example used in this case is for a vibrational-rotational excitation process, H2(v = 0,7 = 0) H2(v =1,/ = 2). 

One of the special rotary atomizers worth mentioning is the windmill type atomizer. In this atomizer, radial cuts are made at the periphery of a disk and the tips of segments are twisted, so that the disk is actually converted into a windmill that can rotate rapidly when exposed to an air flow at aircraft flight speed. The windmill type atomizer has been demonstrated 1171 to be an ideal rotary atomizer for generating a narrow spectrum of droplet sizes in the range most suitable for aerial applications of pesticides at relatively high liquid flow rates. 

With the available high-power lasers the nonlinear response of matter to incident radiation can be studied. We will briefly discuss as examples the stimulated Raman effect, which can be used to investigate induced vibrational and rotational Raman spectra in solids, liquids or gases, and the inverse Raman effect which allows rapid analysis of a total Raman spectrum. A review of the applications of these and other nonlinear effects to Raman spectroscopy has been given by Schrotter2i4)... 

Some aspects of the chemistry of helicenes require still more attention. Since the interpretation of the mass spectrum of hexahelicene by Dougherty 159) no further systematic work has been done on the mass spectroscopy of helicenes, to verify the concept of an intramolecular Diels-Alder reaction in the molecular ion. Though the optical rotation of a number of helicenes is known and the regular increase of the optical rotation with increasing number of benzene rings has been shown, the dependence of the rotation on the helicity is still unknown. The asymmetric induction in the synthesis of helicenes by chiral solvents, or in liquid crystals, though small, deserves still more attention because application to other organic compounds will be promoted when the explanation of observed effects is more improved. 

---