OH stretching modes

Figure Bl.5.15 SFG spectrum for the water/air interface at 40 °C using the ssp polarization combination (s-, s- and p-polarized sum-frequency signal, visible input and infrared input beams, respectively). The peaks correspond to OH stretching modes. (After [ ].)...

Four IR absorption bands have been identified in the spectrum of the hydroxysulfonyl radical (HOSO 2) which has been obtained by the reaction of hydroxyl radicals with sulfur dioxide in argon matrix at 11 K16. The observed bands at 3539.9 and 759.5 cm 1 have been assigned to O—H and S—OH stretching modes while the bands at 1309.2 and 1097.3 cm-1 have been assigned to the asymmetric and symmetric stretching modes of the double bonded S02 moiety. These data are consistent with the theoretical prediction on the geometry of the hydroxysulfonyl radical12. 

The utilization of IR spectroscopy is very important in the characterization of pseudopolymorphic systems, especially hydrates. It has been used to study the pseudopolymorphic systems SQ-33600 [36], mefloquine hydrochloride [37], ranitidine HC1 [38], carbovir [39], and paroxetine hydrochloride [40]. In the case of SQ-33600 [36], humidity-dependent changes in the crystal properties of the disodium salt of this new HMG-CoA reductase inhibitor were characterized by a combination of physical analytical techniques. Three crystalline solid hydrates were identified, each having a definite stability over a range of humidity. Diffuse reflectance IR spectra were acquired on SQ-33600 material exposed to different relative humidity (RH) conditions. A sharp absorption band at 3640 cm-1 was indicative of the OH stretching mode associated with either strongly bound or crystalline water (Fig. 5A). The sharpness of the band is evidence of a bound species even at the lowest levels of moisture content. The bound nature of this water contained in low-moisture samples was confirmed by variable-temperature (VT) diffuse reflectance studies. As shown in Fig. 5B, the 3640 cm-1 peak progressively decreased in intensity upon thermal... 

The superionic phase has been explored with more extensive CPMD simulations.69 Calculated power spectra (i.e., the vibrational density of states or VDOS) have been compared with measured experimental Raman spectra68 at pressures up to 55 GPa and temperatures of 1500 K. The agreement between theory and experiment was very good. In particular, weakening and broadening of the OH stretch mode at 55 GPa was found both theoretically and experimentally. 

R. Wugt Larsen, P. Zielke, and M. A. Suhm. Hydrogen bonded OH stretching modes of methanol clusters A combined IR and Raman isotopomer study. J. Chem. Phys. 126, 194307 (2007). 

Secondly, the emission of a particular complex species is characteristic of that species and can be used to identify the species present. Particularly is this so if excited state lifetimes are measured, as these vary dramatically depending on the number of OH groups coordinated to the Eu3+ or Tb3+ ion. This is because multiple excitation of the OH stretching mode provides an alternative deexcitation route. Measurement of lifetimes thus can be used to determine the number of coordinated water molecules.218... 

These conclusions were ratified in a second paper134 which includes also 2,4-dithiouracil. The appearance of the N1H and/or N3H stretches and the absence of the SH and OH stretches in the spectrum of 2- and 4-thiouracil confirmed that these molecules exist only in the oxo-thione form. Similar findings for 2,4-dithiouracil showed that this molecule exists only as a dithione tautomeric form in an inert matrix. The spectra of S-methylated thiouracils are substantially different they present an absorption in the typical NH stretching range and another one near 3570 cm-1, which is the region characteristic for the OH stretching modes. 

Fig. 4. The frequency shift Ad of the OH stretching mode over the maximum Ad in linear H-bonds as a function of the H-bond angle /3. This figure also gives the angle dependence of the H-bond energy AH (AH Ad)...

Fig. 14.7. High resolution Raman spectrum for D20 excited with a 171 nm photon. Local mode assignment is used the first two quantum numbers indicate the OH stretching modes, the plus sign indicates the symmetry, and the third number represents the bending quantum number. The latter is zero in all cases and therefore not mentioned in the text. The energies are measured with respect to the 00+0) vibrational ground state. Reproduced from Sension et al. (1990).

Some time-dependent data are depicted in Fig. 14c,d. From a comparison of model computations with the measured temporal evolution of the induced bleaching (isotropic component, Fig. 14c) as well as the ESA (Fig. 14d) directly related to excited state population, we infer a lifetime of the OH-stretching mode of I) = 8 1 ps for the dissolved ethanol monomers. From the anisotropic signal component measured in the same experimental runs we determine the reorientation time to be ror = 2 0.5 ps at room temperature. 

For each associate of length L the absorption frequency of the OH-stretching mode depends on the position n in the chain, i.e., on the H-bond strength. In accordance with the literature, we assume end groups with proton acceptor function to show up in the spectrum like ethanol monomers with absorption at 3633 cm 1 independent on the chain length. The frequency position of the proton donor end group of 3500 cm 1 is kept constant in the same way. 

---