Water spectroscopic signatures

It has been known for some time that the spectroscopic signature of Ob-vacs can be healed by exposure to 02 [42-46], In addition, Epling etal. [47] show that temperature-programmed desorption (TPD) spectra of water and ammonia are perturbed when the surface is predosed with 02. This implies that oxygen is left on the surface in some form when Ob-vacs are healed by 02, As such, Epling et al. proposed that one Ob-vac is healed per 02 molecule with the other O atom being adsorbed at a Ti5c site (Oad), a dissociation mechanism supported by theoretical calculations [48, 49]. 

Water clusters containing simple ions are another area of current experimental and theoretical interest. Accordingly, they are also the subject of EA studies. Chaudhury et al. [113] have used EA methods on empirical potentials to obtain optimized structures of halide ions in water clusters, which they then subjected to AMI calculations for simulation of spectra. EA applications to alkali cations in TIP4P water clusters [114,115] have led to explanations of experimental mass-spectroscopic signatures of these systems, in particular the lack of magic numbers for the sodium case and some of the typical magic numbers of the potassium and cesium cases, and the role of dodecahedral clathrate structures in these species. 

A. Lagutschenkov, G.S. Fanourgakis, G. Niedner-Schatteburg, and S.S. Xantheas, The spectroscopic signature of the all-surface to internally solvated structural transition in water clusters in the n = 17 21 size regime, J. Chem. Phys. 122 (2005). 

Infrared interrogation of thin film water contains two important levels of information. The first is from the spectroscopic signature that can provide insight into the nature of the hydrogen bonding networks. Second, the extent of the spectroscopic response (absorption, reflection or extinction) yields an estimate of the film thicknesses for construction of isotherms and through them thermodynamic properties. 

In order to understand the spectroscopic signatures of water, we shortly intfoduce some concepts how molecular spectra can be understood and interpreted. In the Bom-Oppenheimer Approximation it is assumed that the motions of the electrons and the nuclei of a molecule can be separated. If r, denotes the positions of the electrons i and Ry the positions of the nuclei j, then the wavefunctions are given by... 

Now, since the first extrasolar planetary systems have been detected, the search for water on such objects has just started. Because from observations it is very difficult to measure the spectroscopic signatures of the atmospheres of such planets, we have to wait for the newly planned observational facilities (both in space and on ground) some of them will be in operation very soon. 

Carrel, T.G., Tyryshkin, A.M., and Dismukes, G.C. (2002) An evaluation of structural models for the photosynthetic water-oxidizing complex derived from spectroscopic and X-ray diffraction signatures, J. Biol. Inorg. Chem., 7, 2-22. 

Fig. 5.1 P450 ferric-heme interactions at the sixth axial coordination site with various ligands, a Resting state with an active site water molecule bound b Triazole nitrogen coordination associated with the spectroscopic type II signature c Pseudo or type Il-like binding via...

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