Branches rotation-vibration spectra

Figure 4.3-7 Rotation-vibration spectrum of C2H2 (5 hPa, 25 °C, l(i cm) at a spectral resolution of 0,05 cm with the inset the intensity alternation due to spin statistics in the /5-fundamenlal is illustrated (the underlying fine structure is from a hot band transition with its 0-branch shifted to lower wavenumbers compared to the fundamental).

Figure 4.3-9 Rotation-vibration spectrum of NH3 (7.5 hPa, 25 C, 10 cm) at a spectral resolution of 0.05 cm the /f-structure of the / -branch lines of the r 2"f t damental can easily be resolved (see inset). 2...

The VCD spectrum of (S)-(-)-epoxypropane [10] in the liquid and in the gaseous phase shows the splitting of the degenerate vibrational modes of the methyl group. Its analysis verified the VCD theory of the perturbed vibrational degenerate modes. Using a resolution of 1 cm i, the CD in the rotational-vibrational spectrum of (R)-(-h)-methyloxirane has been measured with the result that the Q branch in some bands has the opposite sign to the R and P branches. This can be explained if methyloxirane (in spite of its chirality) is an approximate symmetrical top. 

Figure 6.9 The 1-0 Stokes vibrational Raman spectrum of CO showing the 0-, Q-, and 5-branch rotational structure...

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. 

Temkin S. I., Burshtein A. I. Pressure-induced transformation of the Q-branch of the rotational-vibrational Raman-scattering spectrum, JETP Lett. 24, 86-9 (1976) [Pis ma ZhETFU, 99-103 (1976)]. 

Figure 4.3-24 Part of the pure rotational Raman spectrum of CO2 at a pressure of 10 kPa. Slitwidth 0.21 cm, scanning speed 0.2 cm /min, laser power 8 W at 514.5 nm. The S-branch lines of the molecules in the vibrational ground state are off scale (Altmann et al., 1976).

An example for high-resolution IRS is given in Fig. 6.1-26, where the uj 0-branch of CH3D is displayed. This spectrum has been recorded with the quasi-cw inverse Raman spectrometer developed by Bermejo et al. (1990) whose. schematic arrangement is shown in Fig. 3.6-15 and described in Sec. 3.6.2.3. It represents a Doppler-limited spectrum of the C-D stretching band. The authors were able to assign the observed transitions by performing a theoretical fit to the observed data which allowed them to refine some of the rotational-vibrational constants. 

Figure 10.5 Rotation/vibration levels of carbon monoxide. V and J are the quantum numbers of vibration and rotation. The fundamental vibration corresponds to V = +l and 7 = +1. (a) A rotation-vibration band corresponds to all of the allowed quantum transitions. If the scale of the diagram is in cm , the arrows correspond to the wavenumbers of the absorptions (b) branch R corresponds to A7 = +1 and the band P to A7 = — 1. They are situated either side of band Q, absent from the spectrum (here it can be supposed that A7 = 0 corresponding to a forbidden transition) (c) below, vibration-rotation absorption band of carbon monoxide (pressure of 1000 Pa). The various lines illustrate the principle of the selection rules. The difference (wavenumbers) between successive rotational peaks are not constant due to anharmonicity factors.

In Fig. 10 an experimental rotation-vibrational CARS-spectrum (Q-branch of N2) from the burner is shown as a solid line curve. The best fit for T 1793 K is plotted as a dashed line. To get a flame profile the height of the burner relative to the laser beam axis was varied in steps of 0.25 mm. Each CARS spectrum takes 10 - 15 min. In Fig. 11 the measured temperature points are presented as circles. The theroretlcal curve is shown as dashed line. 

R branch, 364, 365 Radiation, by accelerated charge, 6 by electric quadrupolc, 39 by magnetic dipole, 39 by oscillating dipole, 43 Raman activity (see Scilection rules) Raman band types,, 366 Raman lines (see Raman spectrum) Raman rotation-vibration spectra, 365 Raman scattering, 48, 49 (See also Raman spoctnim)... 

On the contrary, the Q-branch of the anisotropic Raman spectrum broadens monotonously until it merges with the 0-and S-branches (11). The major restriction of these theories is that they are essentially gas phase theories however, this restriction is less stringent for the theory by Burshtein et al. Moreover, the rotation-vibration coupling effects due to intermolecular forces are neglected here again. This is done in the Sobel man theory by neglecting the v-dependence of the S matrix. 

For the case that there are not too many constituents in the gas under investigation, the use of the pure rotational CARS technique may be superior to vibrational CARS thermometry since the spectra are easily resolvable (for N2 the adjacent rotational peaks have a spacing of approximately 8 cm i) compared with the congestion of the rotational lines in the vibrational bands of the Q-branch spectra (see Figure 11). An experimental comparison of rotational and vibrational CARS techniques, under similar conditions has been made that demonstrates that rotational CARS may be viable for flame-temperature measurements up to 2000 K. Of course, the pure rotational approach cannot be applied for spherical molecules which have no pure rotational CARS spectrum. An elegant method, using Fourier analysis based on the periodicity of pure rotational CARS spectra has been introduced recently. 

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