Vibrational overtone spectra

Boyarkine O V, Settle RDF and Rizzo T R 1995 Vibrational overtone spectra of jet-cooled CFgH by infrared laser assisted photofragment spectroscopy Ber. Bunsenges. Rhys. Chem. 99 504-13... 

The propagation in phase space can also be probed in the frequency domain via the vibrational overtone spectra of polyatomic molecules. [30, 34] The separation of time scales can be demonstrated in this fashion and is useful in representing such spectra by the maximal entropy method. [30] Further details can be found in two recent tutorial reviews in Refs. [23] and [24]. 

THE INTERPRETATION OF VIBRATIONAL OVERTONE SPECTRA OBSERVED BY FOURIER TRANSFORM AND LASER PHOTOACOUSTIC SPECTROSCOPY. 

Vibrational overtone spectra are obtained using an infrared pump-ultraviolet probe technique. The OH-Ar complexes are prepared with two quanta of OH stretch (vqh=2) by direct overtone pumping using tunable infrared radiation at 1.4 pm ( 7000 cm" ). The infrared is generated by Raman shifting (second Stokes) the output of a NdrYAG pumped dye laser. The OH-Ar (vqh=2) complexes are then probed by ultraviolet laser-induced fluorescence on OH-Ar transitions located near the OH 1-2 transition, as outlined above. 

Shaji S., Eappen S. M Rasheed T. M. A, and Nair K. P. R., NIR vibrational overtone spectra of N-methylaniline, lV,lV-dimethylaniline and N,N-diethylaniline A conformational structural analysis using local mode model, Spectrochim. Acta A Mol Blomol. Spectrosc., 60, 351-355 (2004). 

Saar BG, O Donoghue GP, Steeves AH, John W Thoman J (2006) Evidence for a blue-shifting intramolecular hydrogen bond in the vibrational overtone spectrum of 1 H-nonafluorobutane. Chem Phys Lett 417 159-163... 

Numerical analysis of the results of studies of SF, excitation in the mode by intense CO2 laser radiation based on a triply degenerate oscillator model t Vibrational overtone spectrum of gaseous SF at 193 K Theoretical study of homogeneous linewidths in SF deduced from experimental IRMPE studies at 944.2 cm . IVR rates and sensitivity to rovibrational distribution... 

The vibrational overtone spectrum of OH-Ar complexes shown in Fig. 6 has been obtained by fixing the ultraviolet probe laser on an OH-Ar excitation feature associated with the OH A(v =l) - X(v"=2) transition, while the infrared pump laser was scanned. The ultraviolet laser was fixed on the Qi bandhead, probing the N=1 to 4 levels of the vibrationally excited complex OH-Ar (vqh=2). The infrared spectrum exhibits a distinctive P, Q, R branch structure, centered at 6970.4 0.2 cm", characteristic of the vibration-rotation spectrum of a molecule with electronic angular momentum (A > 0) in its ground electronic state. A linear OH-Ar complex will have the same ground state symmetry label as OH, namely IT. 

Whether SnFLt is a symmetric or spherical top was discussed based on the rotational spectrum of the sixth stretching vibrational overtone, obtained by photoacoustic spectroscopy107. The IR band at vgn ]q 1844 cm-1 served to investigate the kinetics and mechanism of chemical vapour deposition of a thin tin layer, by thermolysis of trimethylstannane at 378-503 K108. 

Figure 8.4 The v = 6 C-H overtone spectrum as determined by photoacoustic absorption (Hall, 1984) for increasing size alkynes. Each panel contains the molecular formula and the density of vibrational states per cm 1. The band origin does shift some with size but is roughly at 18450 cm"1 for all the molecules shown (see also Kerstel et al., 1991).

Figure 9.40 Cavity ring-down absorption spectrum of HCN showing the 1q3q vibrational overtone/combination band. (Reproduced, with permission, from Romanini, D. and Lehmann, K. K., J. Chem. Phys., 99, 6287, 1993)...

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. 

In the spectra of those alkanes for which a clear gap is observed it is possible to regard 80 cm" as fflh,ax and the spectrum below as that of the lattice vibrations. A complicating feature of the gap region is the presence of lattice vibration overtones, or multiphonon contribution. However, since the lattice fundamentals are not a sequence of individual transitions their overtone intensity appears as a broad contribution. It builds up rapidly from the very lowest frequency to its strongest underneath the TAMs and provides a decreasing background for the LAM region, it has died away completely by about 600 cm". Beyond dodecane the lack of a clear gap makes the upper firequency bound of the external vibrations unidentifiable and we simply assume that the earlier cut-off (fiw = 80 cm ) remains representative. 

Each of these vibrations has a characteristic frequency and can occur at quantized frequencies only. When IR light of the same frequency is incident on the molecule, the energy is absorbed by the molecule and the amplitude of the particular mode increases. However, this absorption occurs only if this vibrational mode can cause a change in the molecular dipole. Consequently, not all vibrational modes are IR active and the molecular symmetry plays a key role in the reduction of IR spectrum patterns. In addition to these fundamental vibrations, overtone peaks may also be observed with much reduced intensity at two, three times, and so on, the wave numbers, the sum of two or three times the wave numbers, or the difference between two wave numbers. Detailed IR spectroscopic theory and group theory can be found elsewhere [60-62]. 

Theoretical determination of force fields may frequently be of assistance. The calculated frequencies are, however, dependent on the level of theory employed. Calculated ab initio harmonic frequencies for furan are sufficiently accurate to help in the assignment of experimental frequencies <88JPC1739> as well as the vibrational overtones <91JPC7659>. In a reinvestigation of the vibrational spectrum of tetrahydrofuran all the normal modes have been identified and assigned in terms of symmetry coordinates with the guidance of the computed ab initio spectrum <93JPC7844>. 

The vibrational absorption spectrum of a polar diatomic molecule consists of a V = 0 1 band, much weaker overtone bands (v = 0 2, 0 —> 3,...), and, if there is significant population of v > 0 levels, hot bands such as v = 1 —> 2,2 —> 3. Each band corresponding to a particular vibrational transition consists of several closely spaced lines. Each such line corresponds to a different change in rotational state simultaneous with the change in vibrational state each line is the result of a vibration-rotation transition. 

Fig. 9.94 Dual frequency comb spectrum of a vibrational overtone band of C2H2 [1341]...

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