Water rotational spectrum

Figure Bl.4.9. Top rotation-tunnelling hyperfine structure in one of the flipping inodes of (020)3 near 3 THz. The small splittings seen in the Q-branch transitions are induced by the bound-free hydrogen atom tiiimelling by the water monomers. Bottom the low-frequency torsional mode structure of the water duner spectrum, includmg a detailed comparison of theoretical calculations of the dynamics with those observed experimentally [ ]. The symbols next to the arrows depict the parallel (A k= 0) versus perpendicular (A = 1) nature of the selection rules in the pseudorotation manifold.

Because simulated water is a classical liquid, the computed power spectrum which describes the translational motions, is bound to disagree with that of real water. Figure 37, shows that the power spectrum has peaks at 44 cm-1 and 215 cm-1, whereas for real water they occur at 60 cm-1 and 170 cm-1. A similar discrepancy exists between simulated and real water rotational power spectra (compare the simulated water frequencies 410 cm-1, 450 cm-1 and 800-925 cm-1 with the accepted experimental values 439 cm-1, 538 cm-1 and 717 cm-1). In this model localization of the molecules around their momentary orientations is only marginal. 

Figure 1.1. Spectrum of electromagnetic radiation A0 - wavelength in free space, W = hu quantum energy, vr - lowest resonance frequency in the rotational spectrum of water, up - plasma frequency of the ionosphere. Reprinted with the permission from [2],...

The interaction between oxetane and water has also been investigated by measuring the rotational spectrum of the 1 1 oxetane-water complex <2004CEJ538>. The rotational spectra of oxetane with H20, D20, DOFI, HOD, and H21sO were studied and quantum-chemical calculations also performed. The water molecule was found to lie in the plane of symmetry of oxetane with the oxetane ring slightly nonplanar. 

An exciting recent development is the work by Endo etal. who reported the detection and analyses of the rotational spectrum of the water-hydroperoxy radical complex. The self reaction of the hydroperoxy radical is a primary source of atmospheric hydrogen peroxide ... 

Microwave absorption spectroscopy has been used to investigate OH, OH and OD produced by electric discharges in the appropriate water vapour . The absorptions lie in the region 7.7 to 37 kMc.sec" and 2uise from transitions between the A-doublets, and (the pure rotation spectrum for OH, a light radical, is in the far infrared). Zeeman modulation was used with a conventional microwave spectrometer. 

Fig. 7. (A) The WEFT sequence in this sequence the tt pulse is applied to rotate all of the magnetization (i.e. both solute and solvent) to the -z-axis. A delay (I>np) of sufficient length is used to allow the water magnetization to relax to the origin ( >np = InfZ) ) whilst during the same period, by virtue of faster longitudinal relaxation, the solute resonances have reached thermal equilibrium. An excitation pulse (represented here as a tj/2 pulse) is then applied and an almost water-free spectrum is acquired. However, in the presence of radiation damping the water quicldy returns nonexponentially to the equilibrium position at a similar rate to the solute nuclei (see Fig. 2). However, if during D p a series of n very weak and evenly spaced gradient pulses are applied so as to inhibit the effects of radiation damping, the water relaxes according to its natural spin-lattice relaxation rate. This is the basis of the Water-PRESS sequence (B). An example of a spectrum obtained with Water-PRESS is shown in Fig. IB and Fig. 6.

Kauppinen, J., Kyro, E. High resolution pure rotational spectrum of water vapor enriched by H2l O and H2l 0, J. Mol. Spectry. 1980, 84,405-23. 

In the far-infrared spectral region water vapour can absorb radiation by transition between different rotational levels without any vibrational or electronic changes. Such a pure rotational spectrum can only be exhibited by a molecule with a permanent dipole moment. The rotational spectrum has been measured for wavelengths up to 2 mm(Herzberg, 1945, p. 58 Furashov, 1966), where this type of absorption ceases and, in good agreement with theory, consists of relatively sharp lines distributed in what looks... 

Fig. 5. Dynamic electrostatic attachment of Fremy s salt dianion to PDADMAC. (a) The CW ESR spectrum (=9.6 GHz) of a 0.5-mA/ solution of in pure water, (jb) Spectrum after addition of PDADMAC with a concentration of 10-mM repeat units, (c) Model of the site-bound state derived from the rotational diffusion tensor and from N ESEEM measurements...

Onsala in 1973. The water molecule H2O, which lias an angle of 105° between the H atoms, has a complex rotational spectrum. Litense maser action has been observed for the 22 GHz transition, wliich is also seen in atmospheric absorption (Fig. 7.24). High-frequency radio astronomy observations have to be performed on dr y days. A large number of other molecules, some of them quite complex, have been observed in space. The (very) remote sensing of the physical conditions in the interstellar clouds has been discussed in [7.93-7.95]. 

Linear molecules have two equal principal moments of inertia, corresponding to rotation about the center of mass about two mutually perpendicular axes, with the third principal moment equal to zero. Nonlinear molecules usually have three different moments of inertia. In this case, the vibration-rotation spectrum can be very complex, even for a simple molecule such as water. The rotational fine stmcture of the H-O-Ti bending mode of water is shown in Figure 1.3. 

As the absorption bands caused by water vapor (its rotational spectrum) are intense throughout the far-infrared region, it is important to purge efficiently the inside of the spectrometer with dried air or nitrogen. Some commercial spectrometers can be evacuated, but usually their sample compartment needs to be purged with dried air or nitrogen. This is commonly needed also in terahertz time-domain spectrometry, which is described in the following section. 

In Figure 19.5, a high-resolution absorption spectrum (rotational spectrum) of water vapor in the atmosphere at a reduced pressure of 60 Pa is shown, together with the measured THz-TDS signal shown in (a). The abscissa range shown in (b) and (c) covers 0-150 cm , although the spectrum actually measured covers a region from about 1.3 to 230 cm The phase-delay spectrum is also shown in (c), but it does not have any particular analytically useful information. The instrument used for this spectral measurement was manufactured... 

Figure 19.5 TFIz-TDS measurement of the rotational spectrum of water vapor, (a) Measured Interference signal Intensity In arbitrary unit, (b) transmission spectra of 0 vacuum and (g) water vapor in the atmosphere at a reduced pressure of 60 Pa, and (c) absorbance and phase-delay spectra of water vapor In the atmosphere at a reduced pressure of 60 Pa.

The external reflection of infrared radiation can be used to characterize the thickness and orientation of adsorbates on metal surfaces. Buontempo and Rice [153-155] have recently extended this technique to molecules at dielectric surfaces, including Langmuir monolayers at the air-water interface. Analysis of the dichroic ratio, the ratio of reflectivity parallel to the plane of incidence (p-polarization) to that perpendicular to it (.r-polarization) allows evaluation of the molecular orientation in terms of a tilt angle and rotation around the backbone [153]. An example of the p-polarized reflection spectrum for stearyl alcohol is shown in Fig. IV-13. Unfortunately, quantitative analysis of the experimental measurements of the antisymmetric CH2 stretch for heneicosanol [153,155] stearly alcohol [154] and tetracosanoic [156] monolayers is made difflcult by the scatter in the IR peak heights. 

The cation of 4,4 -biquinazolinyl and its 2,2 -dimethyl derivative readily add water across the 3,4- and 3, 4 -double bonds, but the cation of 2,2 -biquinazolinyl is not hydrated. Hydration in the 4,4 -isomers has been attributed to restricted rotation about the 4,4 -bond, a steric effect which is relieved by hydration. The ultraviolet spectrum of 2,2 -biquinazolinyl (neutral species and cation) shows that there is considerable conjugation between the quinazoline groups. Covalent hydration is absent from the latter compound because it would otherwise destroy the extended conjugation present. 

Properties of panal (Nakamura etal., 1988a). Purified panal is a colorless, amorphous solid, soluble in alcohols, water, ethyl acetate, and chloroform. The absorption spectrum (Fig. 9.3) shows a single peak (A.max 217nm, e 15,300). Optical rotation [a]D —17° (c 0.9, methanol). Mass spectrometry and NMR analysis showed that panal is a sesquiterpene aldehyde, C15H18O5 (Mr 278.30), with the structure shown below. 

The overall OD vibrational distribution from the HOD photodissociation resembles that from the D2O photodissociation. Similarly, the OH vibrational distribution from the HOD photodissociation is similar to that from the H2O photodissociation. There are, however, notable differences for the OD products from HOD and D2O, similarly for the OH products from HOD and H2O. It is also clear that rotational temperatures are all quite cold for all OH (OD) products. From the above experimental results, the branching ratio of the H and D product channels from the HOD photodissociation can be estimated, since the mixed sample of H2O and D2O with 1 1 ratio can quickly reach equilibrium with the exact ratios of H2O, HOD and D2O known to be 1 2 1. Because the absorption spectrum of H2O at 157nm is a broadband transition, we can reasonably assume that the absorption cross-sections are the same for the three water isotopomer molecules. It is also quite obvious that the quantum yield of these molecules at 157 nm excitation should be unity since the A1B surface is purely repulsive and is not coupled to any other electronic surfaces. From the above measurement of the H-atom products from the mixed sample, the ratio of the H-atom products from HOD and H2O is determined to be 1.27. If we assume the quantum yield for H2O at 157 is unity, the quantum yield for the H production should be 0.64 (i.e. 1.27 divided by 2) since the HOD concentration is twice that of H2O in the mixed sample. Similarly, from the above measurement of the D-atom product from the mixed sample, we can actually determine the ratio of the D-atom products from HOD and D2O to be 0.52. Using the same assumption that the quantum yield of the D2O photodissociation at 157 nm is unity, the quantum yield of the D-atom production from the HOD photodissociation at 157 nm is determined to be 0.26. Therefore the total quantum yield for the H and D products from HOD is 0.64 + 0.26 = 0.90. This is a little bit smaller ( 10%) than 1 since the total quantum yield of the H and D productions from the HOD photodissociation should be unity because no other dissociation channel is present for the HOD photodissociation other than the H and D atom elimination processes. There are a couple of sources of error, however, in this estimation (a) the assumption that the absorption cross-sections of all three water isotopomers at 157 nm are exactly the same, and (b) the accuracy of the volume mixture in the... 

Fig. 1.6 Absorption spectrum for water (gaseous, solution, and liquid). Above the vapor band is Mecke s rotational analysis [11,12].

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