Vibrations combination

The illustration of various types of vibronic transitions in Figure 7.18 suggests that we can use the method of combination differences to obtain the separations of vibrational levels from observed transition wavenumbers. This method was introduced in Section 6.1.4.1 and was applied to obtaining rotational constants for two combining vibrational states. The method works on the simple principle that, if two transitions have an upper level in common, their wavenumber difference is a function of lower state parameters only, and vice versa if they have a lower level in common. 

The IR (and Raman) spectra of 1,2-benzisoxazole and 2,1-benzisoxazole have been recorded and their fundamental and combined vibrations assigned (80MI41604). Similar studies have been carried out with 2,1-benzisoxazolium salts (74DIS(B)147, 71JOC1543). 

Observed on the wing of the CS2 bending mode. Occurs in violation of the selection rules of the point group Dsd but is IR active under the Csi factor group of the crystal. Could also be a combination vibration or caused by the CS2 impurity which was present in the sample (see text)... 

The target molecule C2S 111 was generated by laser-induced photolysis of matrix-isolated C3S2 110 or C3OS 112. Two of the three fundamental vibrations of 111 are observed directly at 1666.6 and 862.7 cm-1, and from an overtone and a combination vibration the position of the missing bending mode in the... 

S. Jarmelo, N. Maiti, V. Anderson, P. R. Carey, and R. Fausto, Ca H bond stretching frequency in alcohols as a probe of hydrogen bonding strength A combined vibrational spectroscopic and theoretical study of n [1 Djpropanol. J. Phys. Chem. A 109, 2069 2077 (2005). 

Bands arising in the spectra of condensed thiophenesS s in the region 2000-1666 cm S arise from overtone or combination vibrations due... 

When absorption is caused by more than one fundamental vibration, the sum or difference of multiples of their fundamental vibration wavenumbers are observed. This is the so-called "absorption due to combination vibration", and the wavenumber Vc is obtained by using the following equation ... 

The orientation dependence of the PES couples the rotational states of the molecules, consequently the scattered flux should show strong rotational excitation and de-excitation. For late barrier systems this also couples to vibrational motion, i.e. there are combined vibrational and rotational transitions. We shall return to this topic in Sections 5 and 6. 

The resonance Raman spectrum of a thin film of selenium exhibits 10 signals in the region 115-1400 cm-1, which have been assigned to the fundamentals P2(ai) and vio(e3) of Seg and to their overtones and combination vibrations 44). 

Eight combination vibrations and overtones, respectively, have been observed in the rR spectrum of Se42+ in 25% oleum, and these have been used to calculate the harmonic wave number coi = 321.8 0.5 cm-1 and the anharmonicity constants Xu = -0.55 andx42 = -1.3 cm-1 (76). Because of the high molecular symmetry, the spectroscopic data are insufficient to calculate accurate force constants, but when most of the interaction constants are neglected (i.e., set equal to zero) the following force constants for Se42+ can be deduced (in N/cm) (70, 76) ... 

The characteristic pattern of overtone bands and combination vibrations between 2000 and 1660 cm in the IR spectra of alkyl substituted benzene derivatives as well as the out-of-plane deformation vibrations of the hydrogen atoms in the IR spectra are frequently less reliable as indicators of the substitution pattern, especially in the presence of polar substituents, in which case their position tends to shift, and they often overlap with bands of substituents. 

Absorption bands that are attributed to overtone and combination vibrations are also observed in the IR spectrum of polyatomic molecules. Overtone vibrations occur at frequencies of approximately integral multiples of the fundamental frequencies. Combination vibrations appear at frequencies that are the sum or the difference of the frequencies of two or more frmdamental vibrations. Overtone and combination bands are much less intense than fundamental bands. 

Fermi resonance, which is the interaction between frmdamental vibrations and overtone or combination vibrations, is also common in IR spectra. The result of Fermi resonance is the formation of two new vibration modes with one frequency higher and the... 

Figure 16.13. UV/visible video image and IR re-construclion of four polyslyrene resin beads with a diameter of about 80 pm. The IR map was obtained with a motor-driven x-y stage in combination with an IR microscope. For the reconstruction of the resin beads the integral of the polyslyrene combination vibration at 1942 cm-1 was used (Reproduced from [25]).

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