Proton transfer, hydrogen bonds molecular associates

A special type of pseudo-polymorphism is that related to the proton transfer along an X-H Y interaction. The motion may not be associated with a phase transition, but may well imply the transformation of a molecular crystal into a molecular salt. Wilson [34] has discussed, on the basis of an elegant neutron diffraction study, the migration of the proton along an O-H O bond in a co-crystal urea-phosphoric acid (1 1) whereby the proton migrates towards the mid-point of the hydrogen bond as the temperature is increased, becoming essentially centred at T > 300 K. Wiechert and Mootz [35] isolated two crystalline materials composed of pyridine and formic acid of different composition. In the 1 1 co-crystal the formic acid molecule retains its proton and transfer to the basic N-atom on the... 

Abstract Far-ultraviolet (FUV) absorption spectroscopy provides molecular information about valence electronic transitions a, n, and Jt electron excitation and charge transfer (CT). FUV spectral measurements of liquid water and aqueous solutions had been limited, because the absorptivity of liquid water is very intense (absorptivity 10 cm at 150 nm). We have developed an attenuated total reflection (ATR)-type FUV spectrophotometer in order to measure FUV spectra of liquid water and aqueous solutions. The ATR-FUV spectroscopy reveals the features of the valence electronic transition of liquid water. This chapter introduces a brief overview of the first electronic transition (A. Y) of liquid water (Sect. 4.1) and the FUV spectral analyses (140-300 nm) of various aqueous solutions including how the hydrogen bonding interaction of liquid water affects the A <— X transition of water molecules (Sect. 4.1) how the A Y bands of water molecules in Groups 1, 11, xm, and lanthanoid (Ln +) electrolyte solutions are associated with the hydration states of the metal cations (Sects. 4.2 and 4.3) how the protonation states of amino acids in aqueous solutions affect the electronic transition of the amino acids (Sect. 4.4) and the analysis of O3 pulse-photolytic reaction in aqueous solution using a nanosecond pump-probe transient FUV spectrophotometer (Sect. 4.5). 

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