Weakly bound clusters

The 3 1 LDAO/SDS mixture becomes viscoelastic and rheo-pectic when a small amount of NaCl Is added. Its viscosity shows a reversible Increase with time of shearing at constant shear rate. The rheopectic behavior Is probably due to long thread-like micelles that are aligned parallel to the flow In weakly bound clusters, as In the case of cetyltrlmethyl ammonium bromide and monosubstituted phenol mixed solutions (21). 

G. S. Tschumper, Multicentered integrated QM QM methods for weakly bound clusters An efficient and accurate 2-body many-body treatment of hydrogen bonding and van der waals interactions, Chem. Phys. Lett., 427 (2006) 185-191. 

One interesting challenge that reactions in van der Waals and hydrogen-bonded clusters offer is the possibility of studying specifically how weak interactions or microsolvation bonds affect a chemical reaction or dissociation process. In that sense, theoretical studies of weakly bound clusters have proved to be useful in learning about the crossover in behavior from that of an isolated nonsolvated molecule in the gas phase to that for a molecule in a liquid or solid solvent. 

Density functional theory (DFT) [62] incorporates electron correlation at a very small computational cost, but its suitability for weak interaction still seems a somewhat open question. There have been comparisons of DFT and conventional methods [63 68]. Mostly, an improvement over SCF level treatment seems possible, but there is a clear dependence on the choice of functional and on basis-set size. Also, DFT may be more sensitive to BSSE in smaller basis sets than conventional treatments [64]. A single functional choice for spectroscopic accuracy in treating weakly bound clusters does not yet seem at hand, but that alone does not preclude application of DFT for lower levels of accuracy. With the computational cost advantage of DFT, the capability exists for treating large, extended clusters. 

D. M. Benoit, A. X. Chavagnac, and D. C. Clary, Speed improvement of diffusion quantum Monte Carlo calculations on weakly bound clusters, Chem. Phys. Lett. 283, 269-276 (1998). 

The optothermal spectrum will faithfully represent the absorption spectrum provided that the molecules do not fluoresce prior to arrival at the detector. Fluorescence is not a problem because infrared fluorescence lifetimes are of the order of milliseconds. The transit time from the laser-molecular beam interaction region to the detector is tens of ps. Furthermore, it is possible to determine if the absorbing species is a stable monomer, or weakly bound cluster. When a stable monomer absorbs a photon, the amount of energy measured by the bolometer increases. When a weakly-bound species absorbs a photon greater than the dissociation energy, vibrational predissociation will take place and the dissociating fragments will not hit the bolometer element. 

---