Far infrared study of the benzene-iodine complex

Abstract

A theory of the lineshape of the infrared spectra of weak charge transfer complexes which emphasizes only the electrostatic interactions--namely quadrupole-induced dipole interactions--between the acceptor and donor molecules is presented and applied to the iodine-benzene complex in dilute solutions.For this complex, it is predicted that the I.R. spectra result from a weighted sum of an induced low frequency profile centred at about 100cm -1, with the profile centred at the iodine stretching frequency (205 cm-l) resulting from the convolution operation of an induced profile with the vibrational profile associated with the iodine molecule. These induced profiles are the same if the rotational motions of benzene and iodine are identical.The experimental data are analysed within the framework of this theory using for this purpose the iodine vibrational profile estimated from Raman measurements and Mori's three-variable profiles for the induced ones. The best agreement is obtained using two different induced profiles for the high and low frequency spectra, the correlation times of which differ by about an order of magnitude; the shorter one being associated with the very low frequency I.R. profile. This result might suggest that the rotational behaviour of the benzene and iodine molecules are very different in contradiction with Raman observations. It is thus argued that these spectra reflect different temporal aspects of the very complex auto-correlation function (a.c.f.) of the induced dipole moment of the system.The broad band is related to the very fast fluctuations of the induced dipole moment due to local motions of the iodine-benzene cage and provides information on the short time behaviour of the a.c.f. This is seen on the corresponding correlation function which decreases very rapidly with an associated correlation time close to the one observed for collision-induced spectra of liquids composed of non-polar molecules. On the contrary, the correlation function associated with the high frequency vi_ x induced profile decreases more slowly; the value of its correlation time which is of the order of magnitude of the one obtained from dielectric experiments is slightly lower than the rotational correlation times of iodine and benzene molecules. This profile is influenced by the long-time behaviour of the induced dipole moment and depends upon both the orientational motions and the mutual diffusion of the molecules. Hence it might contain information on the life time of the complex.Finally, the theoretical zero and second moments of the spectra associated with the low frequency induced spectral density are calculated. The value which is found for the former is in good agreement with the corresponding experimental one. However it is important to note that the experimental t Author to whom correspondence should be addressed. Downloaded by [New York University] at 07:22 20 June 2015 574 J. Lascombe and M. Besnarddetermination of this quantity is subject to considerable error. The experimental second moment, which is ...

Vibrational relaxation of I2 in complexing solvents: The role of solvent–solute attractive forces

“…It is also quite striking that the experimentally determined G() has a steeper slope than that given by a Mori model. 18 This observation is also consistent within the linearly coupled INM model, for one expects the coupling to the solvent to drop dramatically at the point where the one-phonon solvent density of states drops to zero.…”

“…In the case of benzene-I 2 , the magnitude of charge transfer in the ground state is estimated to be about 0.02 electron charges. 18 The degree of charge transfer can be controlled, however, by substitution on the arene ring. Electron donating methyl groups increase the degree of charge transfer.…”

Photodissociation Dynamics of the Iodine−Arene Charge-Transfer Complex

“…A discrepancy between theory and experiment may also be caused by the inability of the MD program used to describe varying polarization of the I 2 molecule. Part of the binding energy of the I 2 :ben complex is caused by the slight polarization of I 2 by benzene. , This effect also follows from the ab initio results and is incorporated in the MD force field. However, because of the shifted charge, a benzene molecule approaching an I 2 molecule from the other side will be slightly repelled by it.…”

Estimation of the Interaction-Induced Effects on the Far-Infrared and Infrared Correlation Functions of HCl Dissolved in CCl4: A Molecular Dynamics Study

“…In this particular case, it is very interesting to compare our FIR results for the HCl/CCl 4 system with previous published theoretical ones for similar mixtures obtained by other groups. We mention, e.g., the far-IR absorption of the diluted mixtures of HCl, DCl dissolved in liquefied inert gases (Ar, Kr, and Xe) and liquid SF 6 , which have been investigated theoretically 26 (see also ref −19 in ref ). These studies have shown that the induced contributions must be considered in order to reproduce the FIR experimental absorption spectrum of such systems, especially at high densities.…”

“…D (ω) denotes a frequency dependent internal field correction. By assuming that the product η(ω) D (ω) is equal to one, one is lead to conclude that the shape of the absorption spectrum is mainly dominated by the time dependence of the CF C M ( t ), i.e The evaluation of the total dipole moment at time t , M⃗ tot ( t ), is based upon theoretical considerations for the total permanent dipole moment, M⃗ P , of the probe diatomic molecules and the total induced-dipole moment, M⃗ I , − of all of the species in the solution: For our diluted mixture of a certain mole fraction, the total number of molecules, N , contains N A (A = CCl 4 ) solvents and N B (B = HCl) solutes.…”