Molecules van der Waals

LeRoy R J and Carley J S 1980 Spectroscopy and potential energy surfaces of van der Waals molecules Adv. Chem. Phys. 42 353... 

Hutson J M and Howard B J 1980 Spectroscopic properties and potential surfaces for atom-diatom van der Waals molecules Mol. Phys. 41 1123... 

Hutson J M 1990 Intermolecular forces from the spectroscopy of van der Waals molecules Ann. Rev. Phys. Chem. 41 123... 

Buckingham A D and Fowler P W 1983 Do electrostatic interactions predict structures of van der Waals molecules J. Chem. Phys. 79 6426... 

Scheiner S 1997 Hydrogen Bonding A Theoretical Perspective (New York Oxford) A survey of research on hydrogen bonding with emphasis on tiieoretical calculations. 1994 van der Waals molecules Chem. Rev. 94 1721... 

A special issue devoted to review articles on various aspects of van der Waals molecules. 

A covalent bond (or particular nomial mode) in the van der Waals molecule (e.g. the I2 bond in l2-He) can be selectively excited, and what is usually observed experimentally is that the unimolecular dissociation rate constant is orders of magnitude smaller than the RRKM prediction. This is thought to result from weak coupling between the excited high-frequency intramolecular mode and the low-frequency van der Waals intemiolecular modes [83]. This coupling may be highly mode specific. Exciting the two different HE stretch modes in the (HF)2 dimer with one quantum results in lifetimes which differ by a factor of 24 [84]. Other van der Waals molecules studied include (NO)2 [85], NO-HF [ ], and (C2i J )2 [87]. 

As discussed in section A3.12.2. intrinsic non-RRKM behaviour occurs when there is at least one bottleneck for transitions between the reactant molecule s vibrational states, so drat IVR is slow and a microcanonical ensemble over the reactant s phase space is not maintained during the unimolecular reaction. The above discussion of mode-specific decomposition illustrates that there are unimolecular reactions which are intrinsically non-RRKM. Many van der Waals molecules behave in this maimer [4,82]. For example, in an initial microcanonical ensemble for the ( 211 )2 van der Waals molecule both the C2H4—C2H4 intennolecular modes and C2H4 intramolecular modes are excited with equal probabilities. However, this microcanonical ensemble is not maintained as the dimer dissociates. States with energy in the intermolecular modes react more rapidly than do those with the C2H4 intramolecular modes excited [85]. 

Lovejoy C M and Nesbitt D J 1989 Intramolecular dynamics of Van der Waals molecules an extended infrared study of Ar-HF J. Chem. Phys. 91 2790-807... 

Hutson J M 1990 Intermolecular forces from the spectroscopy of Van der Waals molecules Ann. Rev. Phys. Chem. 41 123-54 Huston J M 1991 An introduction to the dynamics of Van der Waals molecules Adv. Mol. Vibrat. Coll. Dyn. 1A 1-45... 

Gerber, R.B., Buch, V., Ratner, M.A. Time-dependent self-consistent field approximation for intramolecular energy transfer. I. Formulation and application to dissociation of van der Waals molecules. J. Chem. Phys. 77 (1982) 3022-3030. 

There is little evidence for 1 1 compounds between elements in this group under normal conditions. The diatomic van der Waals molecules, CaMg, SrMg and SrCa, however, have been synthesized by codepositing the atoms from separate sources with argon or krypton into solid matrices at 12 K. These low-T species are identified from their laser-induced fluorescence spectra. The ground-state spectroscopic data for these alkaline-earth dimers form a sensible series between the parent molecules Mg2, Caj and Sr2. ... 

Francoise L-M, Voglet N, Thierry L, Rudi A (2001) Evidence for the emission of alkali-metal-noble-gas van der Waals molecules from cavitation bubbles. Ultrason Sonochem 8(2) 151—158... 

The blue satellite peak associated with resonance line of rubidium (Rb) saturated with a noble gas was closely examined by Lepoint-Mullie et al. [10] They observed SL from RbCl aqueous solution and from a 1-octanol solution of rubidium 1-octanolate saturated with argon or krypton at a frequency of 20 kHz. Figure 13.4 shows the comparison of the SL spectra of the satellite peaks of Rb-Ar and Rb-Kr in water (Fig. 13.4b) and in 1-octanol (Fig. 13.4c) with the gas-phase fluorescence spectra (Fig. 13.4a) associated with the B —> X transition of Rb-Ar and Rb-Kr van der Waals molecules. The positions of the blue satellite peaks obtained in SL experiments, as indicated by arrows, exactly correspond to those obtained in the gas-phase fluorescence experiments. Lepoint-Mullie et al. attributed the blue satellites to B — X transitions of alkali-metal/rare-gas van der Waals species, which suggested that alkali-metal atom emission occurs inside cavitating bubbles. They estimated the intracavity relative density to be 18 from the shift of the resonance line by a similar procedure to that adopted by Sehgal et al. [14],... 

Then, the collisional interactions with rare-gas atoms result in the formation of electronically excited alkali-metal/rare-gas molecules. These van der Waals molecules emit light. Lepoint-Mullie et al. claimed that the site of SL from alkali-metal atoms is in the gas phase inside bubbles and that the SL is chemiluminescence. 

Another important question deals with the intramolecular and unimolecular dynamics of the X-—RY and XR -Y- complexes. The interaction between the ion and molecule in these complexes is weak, similar to the intermolecular interactions for van der Waals molecules with hydrogen-bonding interactions like the hydrogen fluoride and water dimers.16 There are only small changes in the structure and vibrational frequencies of the RY and RX molecules when they form the ion-dipole complexes. In the complex, the vibrational frequencies of the intramolecular modes of the molecule are much higher than are the vibrational frequencies of the intermolecular modes, which are formed when the ion and molecule associate. This is illustrated in Table 1, where the vibrational frequencies for CH3C1 and the Cr-CHjCl complex are compared. Because of the disparity between the frequencies for the intermolecular and intramolecular modes, intramolecular vibrational energy redistribution (IVR) between these two types of modes may be slow in the ion-dipole complex.16... 

Supramolecular aggregations are commonly referred to by a variety of terms, including adduct, complex, and van der Waals molecule. In this chapter we shall primarily employ the more neutral term cluster, which may, if desired, be qualified with the type of intermolecular interaction leading to clustering (e.g., H-bonded cluster ). General and specific types of intermolecular forces are discussed in the following sections. 

Method for Determining Rovibrational Eigenstates of van der Waals Molecules. 

Better determination of overtone and combination bands of familiar molecules and the spectroscopic characterization of new species [radicals (Shida, 1991 Bemath, 1990), ions (Miller and Bondybey, 1983 Leach, 1980), and van der Waals molecules in particular (Nesbitt, 1988 Saykally, 1989 Hutson, 1990 Heaven, 1992)] continue to receive wide attention (Figure 0.3). 

Figure 0.3 The structure of the van der Waals molecule C6H6 Ar as determined by very high-resolution spectroscopy. (Adapted from Weber, van Bargen, Riedle, and Neusser, 1990.) The potential along the C6H6 - Ar stretch motion is shown in Figure 1.4.

A very interesting field of research covers the spectroscopy of van der Waals molecules in search of more detailed information about the long range potential and the polarizability. Raman spectra of van der Waals dimers in argon have been observed and a vibrational frequency shift for I2-molecules from 213 cm" to 197 cm has been measured for I2 -Ar-complexes. 

Apparently there are no experimental data on BeNe. If we fit a Morse function to the parameters we obtain for the dissociation curve, it is estimated that there would be 14-15 bound vibrational states for this Van der Waals molecule. Thus, VB theory predicts the existence of stable gaseous BeNe, if it is cold enough, since Dg is only 2kT for room temperature. 

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