Stretching region

Figure Bl.22.3. RAIRS data in the C-H stretching region from two different self-assembled monolayers, namely, from a monolayer of dioctadecyldisulfide (ODS) on gold (bottom), and from a monolayer of octadecyltrichlorosilane (OTS) on silicon (top). Although the RAIRS surface selection rules for non-metallic substrates are more complex than those which apply to metals, they can still be used to detemiine adsorption geometries. The spectra shown here were, in fact, analysed to yield the tilt (a) and twist (p) angles of the molecular chains in each case with respect to the surface plane (the resulting values are also given in the figure) [40].

Figure Bl.22.6. Raman spectra in the C-H stretching region from 2-butanol (left frame) and 2-butanethiol (right), each either as bulk liquid (top traces) or adsorbed on a rough silver electrode surface (bottom). An analysis of the relative intensities of the different vibrational modes led to tire proposed adsorption structures depicted in the corresponding panels [53], This example illustrates the usefiilness of Raman spectroscopy for the detennination of adsorption geometries, but also points to its main limitation, namely the need to use rough silver surfaces to achieve adequate signal-to-noise levels.

Figure Bl.22.8. Sum-frequency generation (SFG) spectra in the C N stretching region from the air/aqueous acetonitrile interfaces of two solutions with different concentrations. The solid curve is the IR transmission spectrum of neat bulk CH CN, provided here for reference. The polar acetonitrile molecules adopt a specific orientation in the air/water interface with a tilt angle that changes with changing concentration, from 40° from the surface nonnal in dilute solutions (molar fractions less than 0.07) to 70° at higher concentrations. This change is manifested here by the shift in the C N stretching frequency seen by SFG [ ]. SFG is one of the very few teclnhques capable of probing liquid/gas, liquid/liquid, and even liquid/solid interfaces.

A hypsochromic shift of 20-50 cm is observed in the double-bond stretching region, when the enamines are converted to the corresponding iminium salts by the electrophilic addition of a proton at the /3-carbon atom. The shift is accompanied by an enhancement in the intensity of the band. Leonard and co-workers (68,71-74) have used this absorption shift as a diagnostic tool for the determination of the position of the double bond... 

The enamines in which the protonation at the -carbon atom is not allowed due to the lack of coplanarity, or, in other words, the lack of electronic overlap, do not exhibit this characteristic absorption shift. For instance in the case of neostrychnine (134) where the overlap is not permitted since this would involve the formation of a double bond at the bridgehead, there is no appreciable difference in the C—C stretching region of the free amine and its perchlorate salt they absorb at 1666 cm and 1665 cm , respectively (70). 

The structure of the protonated enamines has been investigated by infrared spectroscopy. On protonation there is a characteristic shift of the band in the double-bond stretching region to higher frequencies by 20 to 50 cm with an increased intensity of absorption (6,13,14a). Protonated enamines also show absorption in the ultraviolet at 220-225 m/x due to the iminium structure (14b). This confirms structure 5 for these protonated enamines, because a compound having structure 4 would be expected to have only end absorption as the electrons on nitrogen would not be available for interaction with the n electrons of the double bond. 

In 1951, Witkop et al. interpreted the infrared spectra of quinol-2-and -4-ones to favor the oxo formulation. Since then, many investigators, especially Mason, have reported that potential a- and y-hydroxy compounds show infrared absorption bands in the vN—H (3500-3360 cm ) and vC—O (1780-1550 cm ) regions of the spectrum and, hence, exist predominantly in the oxo form references to this work appear in Table I. A study of the bands which occur in the NH-stretching region of the infrared spectra of a series of substituted pyrid-2-ones and quinol-2-ones also supported an oxo formulation for these compounds. Detailed band assignments have been published for pyrid-2- and -4-one. Mason has reported that solutions of j8-hydroxy compounds in chloroform or carbon tetrachloride show... 

Plutonium(IV) polymer has been examined by infrared spectroscopy (26). One of the prominent features in the infrared spectrum of the polymer is an intense band in the OH stretching region at 3400 cm 1. Upon deuteration, this band shifts to 2400 cm 1. However, it could not be positively assigned to OH vibrations in the polymer due to absorption of water by the KBr pellet. In view of the broad band observed in this same region for I, it now seems likely that the bands observed previously for Pu(IV) polymer are actually due to OH in the polymer. Indeed, we have observed a similar shift in the sharp absorption of U(0H)2S0ir upon deuteration (28). This absorption shifts from 3500 cm 1 to 2600 cm 1. 

A Raman spectrum of p-S is shown in Fig. 29. While the Raman lines in the stretching region (430-520 cm ) are of high intensity, exceeding those... 

Figure 6. Time-resolved Fourier transform emission spectrum in the CO2 asymmetric stretch region from the HCCO + 02 reaction. Only signal from is observed. The fit to the data is...

Figure 10. Vibrational spectra of the [HO—Fe—CHs] insertion intermediate in the O—H stretching region. Spectra are obtained by monitoring loss of argon from IR resonance enhanced photodissociation of the argon-tagged complexes [HO—Fe—CH3] (Ar) (n — 1,2).

Figure 12. Vibrational action spectra of V (OCO) in the OCO antisymmetric stretch region, (a) Spectrum obtained by monitoring depletion in the photofragment produced by irradiation at the vibronic origin at 15,801 cm The IR absorption near 2391.5 cm removes molecules from V[" = 0, leading to an 8% reduction in the fragment yield, (b) Spectrum obtained by monitoring enhancement in the VO+ photofragment signal as the IR laser is tuned, with the visible laser fixed at 15,777 cm (the Vj = 1 v" = 1 transition). The simulated spectrum gives a more precise value of the OCO antisymmetric stretch vibration in V" (OCO) of 2392.0 cm .

The ability to measure changes In an L-B film due to the presence of water vapor Is shown In fig. 7a-g and 8a-g. In this experiment the spectra of 2 monolayers of cadmium arachldate on N1 (tall to tall) are recorded In the presence of 11 torr of water vapor In nitrogen at 30 deg C and compared with the spectra obtained with dry nitrogen. The difference between cadmium arachldate on nickel and on silver Is expected to be small because both films are prepared with the same water bath L-B technique prior to transfer to the metal [16]. In both the hydrated and anhydrous experiments, the gas Is swept continuously through the cell to maintain constant pressure. Figures 7a-g show a sequence of dry and wet L-B film spectra In the C-H stretching region 3000 to 2800 cm-1. The spectra, a, c, e, and g of the anhydrous bllayer show the typical bands of fresh, unheated arachldate monolayers. 

When the gibbsite is dehydrated a structural collapse occurs with a large increase in surface area. The boehmite sample has a nominal surface area of 325 m /g. The infrared spectrum of the boehmite shows distinct structure in the OH stretching region, with two peaks located at 3090 and 3320 cm". There are three features at 1648, 1516 and 1392 cm" that are due to adsorbed water and carbonate, which are removed upon heating the boehmite to 350 0 in hydrogen. 

Figure 1. The Infxexed enieeion spectre of CO2 In the esynmetric stretch region and of CO as a function of 30 is intervals through a 200 ps pulse. The surface teaiperature was 900C and the xesoln tion was 8 cm . ...

Fig. 4 a IR spectra, in the OH stretching region, of from top to bottom, TS-1 samples (full line spectra) with increasing Ti content, from 0 (silicalite-1, dashed spectrum) to 2.64 atoms per imit cell. All samples have been activated at 120 °C. Adapted from [24] with permission. Copyright (2001) by the ACS. b Schematic representation of the preferential location of Ti atoms and Si vacancies in the MFI framework (upper part) and their interplay (lower part). Yellow and red sticks represents Si and O of the regular MFI lattice blue balls refer to Ti, and red and white balls to O and H of defective internal OH groups... 

FigureS.6 CVobtained with a sweep rate ofSOmVs (solid line) and potential dependence of integrated SFC intensity in the OH-stretching region ( ) ofa Pt thin film electrode in 0.1 M HCIO4 solution.

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