Harmonic vibrations hydrogen bonded molecules

Section VI. It is possible to unblock the first drawback (i), if to assume a nonrigidity of a dipole—that is, to propose a polarization model of water. This generalization roughly takes into account specific interactions in water, which govern hydrogen-bond vibrations. The latter determine the absorption R-band in the vicinity of 200 cm-1. A simple modification of the hat-curved model is described, in which a dipole moment of a water molecule is represented as a sum of the constant (p) and of a small quasi-harmonic time-varying part p(/j. 

For numerous ion... polar molecule hydrogen bonded ccanplexes harmonic and anharmonic vibrational frequencies were calculated and compared with observed ones for the respective references see Ref. . A detailed description of calculating vibrational spectra and infrared absorption intensities is given in a study on the (CH3SH)2 dimer " . 

Regarding the longitudinal harmonic vibration of H-bonded charged molecules, we determine A from classical theory as a quantity, which concerns breaking of hydrogen bonds ... 

In liquid water there are a number of eoUeetive inter-molecular vibrational modes, such as the HB excitation around 200 cm, which is like a breathing mode involving displacement of many molecules. Another example is the libration mode at around 600 cm, which is a restricted rotation, due to hydrogen-bonding. These low-frequency modes contribute to the entropy and specific heat of liquid water. But these modes are highly anharmonic, with a short lifetime, so the above description based on a harmonic oscillator cannot be used to describe them. 

ABSTRACT Ground state properties of several conceivable hydrogen bonded trimers composed of HCN and HP molecules have been evaluated at the SCP level. The most stable ones of these trimeric complexes have subsequently been reinvestigated with electron correlation methods (ACPP). We provide a survey of stabilization energies, dipole moments, selected harmonic vibrational frequencies and corresponding infrared intensities. We also discuss various aspects of the non-additivity of intermolecular interaction taking place in these clusters. 

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