Third overtone

Third overtone Second Combination-overtone (SCOT)... 

HOD. A 722.5 nm laser pulse (A,i) excites the third overtone stretch of OH. After a short delay, a pulse of ultraviolet radiation of frequency V2 (wavelength X2) dissociates the molecule, and a third pulse with a wavelength near 308 nm (X3) probes the OH or OD fragments by laser-induced fluorescence. It is observed that with a dissociation wavelength of 266 or 239.5 nm, the products are almost exclusively H + OD,... 

As mentioned above, HOSi(OA)3 may be taken as the simplest cluster model of the terminal hydroxyl group in silicas. Indeed, even with this cluster CNDO/BW provided a quite satisfactory description of the lower part of the curve representing potential energy as a function of the OH stretching vibration coordinate ROH (Fig. 2) (48,49). The respective experimental curve was plotted by Kazansky et al. (49) based on the analysis of the fundamental frequency vOH and the first overtone of the characteristic OH stretching vibration in terms of the Morse potential function. The frequencies of the second and third overtones were also determined in that work, and it was shown that the Morse potential reproduced well the potential curve within a rather wide range of ROH. 

Finally, we like to mention that equivalent to the conventional energy frame KHD formulation, the time-dependent theory of Raman scattering is free from any approximations except the usual second order perturbation method used to derive the KHD expression. When applied to resonance and near resonance Raman scattering, the time-dependent formulation has shown advantages over the static KHD formulation. Apparently, the time-dependent formulation lends itselfs to an interpretation where localized wave packets follow classical-like paths. As an example of the numerical calculation of continuum resonance Raman spectra we show in Fig. 6.1-7 the simulation of the A, = 4 transitions (third overtone) of D excited with Aq = 488.0 nm. Both, the KHD (Eqs. 6.1-2 and 6.1-18) as well as the time-dependent approach (Eqs. 6.1-2 and 6.1-19) very nicely simulate the experimental spectrum which consists mainly of Q- and S-branch transitions (Ganz and Kiefer, 1993b). 

As well as the ab initio potential (equation (4)), the empirical potential from Ref. 8 was also applied in the calculations. First the experimental results [28,29] will be discussed. Both experiments agreed as to the vibrational bands at about 40 and 31 cm"l and assigned them as intermolecular stretch (v ) and first overtone of intermolecular bend (vx, Vy) vibration. The third band at about 62 cm" was assigned either as third overtone of intermolecular bend or first overtone of intermolecular stretching vibration. The later assignment is consistent with a rather large anharmonicity. 

Determined from the first and third overtone and the combination band with the mode la. Calculated from the first overtone of these normal modes. 

For the third overtone, the wave operator method diverges after three iterations. For this reason, the results obtained after either three or four iterations are provided. 

First overtone, C-H stretching Second overtone, C-H stretching Third overtone, C-H stretching Combination bands... 

In another study (13), a semicarbazide coating was prepared by dissolving 100 mg of semicarbazide hydrochloride in 10 ml of 1 1 acetone/ethanol, followed by the addition of 5 ml of 6 M ammonia solution. The clear solution was allowed to stand to ensure neutralization of the hydrochloric acid before application to the crystal electrodes. The coated 9 MHz crystal was driven at its third overtone of 27 MHz. The detector had a sensitivity of 12.4 Hz jjI and a linear response in the concentration range 5.50 tjg 1. the highest response was obtained in a dry nitrogen stream at a flow rate of 90 ml min, and decreased to about 33% in a wet air stream (58% relative humidity) at a flow rate of 200 ml min". The relative sensitivities to the potential intererences studied (chloroform, acetaldehyde, ethanol, acetone, n-octanol, ethyl-butyrate and n-hexylacetate) ranged from 0.000000 to 0.000029 compared to a relative response of one to acetoin. 

For aliphatic hydrocarbons, the first overtones of C-H stretching are observed in the 1600-1800 nm range, the second overtones at 1150-1210 nm and the third overtones at 880-915 nm. NIR spectroscopy may be used to study unsaturated hydrocarbons. Although bands due to C=C and C=C bonds are not directly observed in the near infrared, the bands due to the adjacent C-H bonds may be differentiated from saturated hydrocarbons. 

Figure 3. Changes in the normalized third overtone resonance frequency, (black line), and dissipation, AD (gray line), during adsorption of PLL(20)-g[3.5]-PEG(5) onto a Si02 sputter-coated surface for the HEPES—methanol system (polymer injection at arrow number 2). Before injection of the polymer the baseline of the Si02-coated quartz crystal was measured in methanol and subsequently in HEPES buffer solution. The exchange of methanol for HEPES buffer solution is indicated by the arrow number 1. The measurement chamber was rinsed with polymer-free aqueous HEPES buffer solution 30 min after polymer injection (arrow number 3). Subsequently, the aqueous HEPES buffer solution was replaced by methanol, and the resonance frequency fo and the dissipation factor D were measured again (arrow number 4). The reproducibility of the A/o and KD shifts upon solvent changes was tested by replacing methanol by aqueous HEPES buffer solution (arrow number 5). This measurement protocol for the methanol solvent system was repeated and applied to the other two solvent systems, ethanol and 2-propanol.

Fignre S. Shift in the resonance frequency of the third overtone of a S102 QCM crystal in 10 vol % MAA solution upon exposure to 365 mn UV-LED irradiation. 

C-H, N-H, and O-H Stretch Absorption Bands for Specific SW-NIR (800-1100 nm) functional groups (Second or Third Overtones). 

Thus, one would expect the first overtone to occur somewhere near 7033 cm or 1422 mn using a simple harmonic oscillator model (to convert to wavelength, use IO h- v [in cm ]. Calculations for wavenumber positions for the first overtone (2v), second overtone (3v), and third overtone (4v) can be estimated with the assumption of a 1-5% frequency shift due to anharmonicity. 

The third overtone vibration of the methyl group appears at 10,953 in hexane. The methyl third overtone in some additional molecules is listed in Table 2.2. Wheeler assigns the fourth overtone s position to be at about 13,400 cm (746 nm). Fang and Swofford list the fifth overtone for a linear alkane methyl group C-H stretch to be at 15,690 cm (637 nm), and the sixth at about 17,890 cm" (560 nm). 

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