Weakly bound complexes

Spectroscopy is the most important experimental source of infomiation on intemiolecular interactions. A wide range of spectroscopic teclmiques is being brought to bear on the problem of weakly bound or van der Waals complexes [94, 95]. Molecular beam microwave spectroscopy, pioneered by Klemperer and refined by Flygare, has been used to detemiine the microwave spectra of a large number of weakly bound complexes and obtain stmctiiral infomiation... 

Waals modes in weakly-bound complexes has been discussed in section BT4. MicroM ave and Terahertz Spectroscopy, and will not be repeated here. 

Optimizing water dimer can be challenging in general, and DFT methods are known to have difficulty with weakly-bound complexes. When your optimization succeeds, make sure that you have found a minimum and not a transition structure by verifying that there are no imaginary frequencies. In the course of developing this exercise, we needed to restart our initial optimization from an improved intermediate step and to use Opt=CalcAII to reach a minimum. 

STABILIZATION OF DIFFERENT CONFORMERS OF WEAKLY BOUND COMPLEXES TO ACCESS VARYING EXCITED-STATE INTERMOLECULAR DYNAMICS... 

Stabilization of Different Conformers of Weakly Bound Complexes to Access Varying Excited-State Intermolecular Dynamics 375 By David S. Boucher and Richard A. Loomis... 

Garcia, A., Cruz, E. M., Sarasola, C., Ugalde, J. M., 1997, Properties of Some Weakly Bound Complexes Obtained with Various Density Functionals , J. Mol. Struct. (Theochem), 397, 191. 

The principal intermolecular donor-acceptor interactions of this weakly bound complex are found to be of 7tcc-OBrBr form (3 x 0.20 kcalmol-1), as illustrated in Fig. 5.41(b). A prominent feature of Br2 (and other heavy halogens) is the nearly pure-p character of the bromine bonding hybrid, resulting in a conspicuous backside lobe on the OBrBr antibond (see Fig. 5.41(b)) that is effective in end-on complexation to the pi-donor face of benzene. The unusually small energy separation between donor and acceptor NBOs,... 

R M. Felker, P. M. Maxton, and M. W. Schaeffer, Nonlinear Raman studies of weakly bound complexes and clusters in molecular beams. Chem. Rev. 94, 1787 1805 (1994). 

A. R. W. McKellar. Infrared spectra of weakly bound complexes and... 

From the systematic work described in the previous sections several features can be outlined. First, hybrid B3LYP and gradient-corrected PWP functionals predict the same qualitative behaviour in the M (Sc, Ti, Ni and Cu) + C02 reactions, but quantitative differences are often found. With respect to the reactivity of the different transition-metal atoms studied here, it has been shown that Cu andNi give weakly bound complexes with C02 while Ti and Sc are able to form MC02 stable complexes and OMCO insertion products. In the first case, the insertion occurs without any energy harrier while in the second, a small barrier of 6 kcaPmol is found. 

Beswick, J.A. and Halberstadt, N. (1993). Dynamics of weakly bound complexes (Kluwer, Dordrecht). 

Halberstadt, N., Beswick, J.A., and Schinke, R. (1991). Rotational distributions in the vibrational predissociation of weakly bound complexes Quasi-classical golden rule treatment, in Half Collision Resonance Phenomena in Molecules Experimental and Theoretical Approaches, ed. M. Garcia-Sucre, G. Raseev, and S.C. Ross (American Institute of Physics, New York). 

As discussed in detail in other chapters of this volume, an important application of weakly bound complexes is in the steric control of chemical reactions (Shin et al. 1991a,b). In these studies, a molecular complex is used as a precursor to provide some control over the reactant geometry. The reaction is initiated by UV... 

To focus the review, it is necessary to pass over some topics which are timely, relevant, and could be included were it not for space limitations. One of these is the area of electron photodetachment as applied to the study of the Franck-Condon region of the neutral PES accessed from the corresponding anion. This approach has been shown to provide information about the transition state region of several bimolecular reactions. This work was pioneered by Neumark and coworkers and an excellent review is already available (Manolopoulos et al. 1993 Neumark 1992). Another noteworthy area is state-to-state studies of vibrational predissociation in weakly bound complexes. Miller and coworkers have made impressive advances in which fully state and angle-resolved product distributions have been obtained (Bemish et al. 1994 Block et al. 1992 Bohac et al. 1986, 1992a,b Bohac and Miller 1993a,b Dayton et al. 1989), and these results have been used to bring theory and experiment into accord. The present review is limited to cases in which ultraviolet photodissociation of a complexed moiety initiates reaction. 

The best means of determining the geometric properties of weakly bound complexes is high resolution spectroscopy in combination with theoretical models that treat explicitly the large amplitude motions. However, in some cases structural properties can also be determined with acceptable accuracy by using theory alone. Specifically, semiempirical methods based oh the concepts of classical electrostatics are known to give reliable results, as has been shown, for example, by Dykstra (1990) and coworkers. In most cases, these semiempirical approaches are at least as accurate as the brute force application of large scale ab initio methods to calculate the weak interaction directly. However, even with these semiempirical approaches there is a reluctance to go to the heavier elements because accurate electronic structure calculations are usually needed to provide properties such as... 

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