Van der Waals compound
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A Van der Waals molecule is a weakly bound complex of
atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, a ...
s or
molecules A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...
held together by intermolecular attractions such as
Van der Waals forces In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and th ...
or by
hydrogen bonds In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...
. The name originated in the beginning of the 1970s when stable molecular clusters were regularly observed in
molecular beam A molecular beam is produced by allowing a gas at higher pressure to expand through a small orifice into a chamber at lower pressure to form a beam of particles (atoms, free radicals, molecules or ions) moving at approximately equal velocities, ...
microwave spectroscopy Microwave spectroscopy is the spectroscopy method that employs microwaves, i.e. electromagnetic radiation at GHz frequencies, for the study of matter. History The ammonia molecule NH3 is shaped like a pyramid 0.38 Å in height, with an equilatera ...
.


Examples

Examples of well-studied vdW molecules are Ar2, H2-Ar, H2O-Ar, benzene-Ar, (H2O)2, and (HF)2. Others include the largest diatomic molecule: He2 and
LiHe LiHe is a compound of helium and lithium. The substance is a cold low-density gas made of Van der Waals molecules, each composed of a helium atom and lithium atom bound by van der Waals force. The preparation of LiHe opens up the possibility to ...
.


Supersonic beam spectroscopy

In (supersonic) molecular beams temperatures are very low (usually less than 5 K). At these low temperatures Van der Waals (vdW) molecules are stable and can be investigated by microwave, far-infrared spectroscopy and other modes of spectroscopy. Also in cold equilibrium gases vdW molecules are formed, albeit in small, temperature dependent concentrations. Rotational and vibrational transitions in vdW molecules have been observed in gases, mainly by UV and IR spectroscopy. Van der Waals molecules are usually very non-rigid and different
versions Version may refer to: Computing * Software version, a set of numbers that identify a unique evolution of a computer program * VERSION (CONFIG.SYS directive), a configuration directive in FreeDOS Music * Cover version * Dub version * Remix * ''Ve ...
are separated by low energy barriers, so that tunneling splittings, observable in far-infrared spectra, are relatively large. Thus, in the far-infrared one may observe intermolecular vibrations, rotations, and tunneling motions of Van der Waals molecules. The VRT spectroscopic study of Van der Waals molecules is one of the most direct routes to the understanding of
intermolecular forces An intermolecular force (IMF) (or secondary force) is the force that mediates interaction between molecules, including the electromagnetic forces of attraction or repulsion which act between atoms and other types of neighbouring particles, e.g. a ...
.


See also

*
Van der Waals radius The van der Waals radius, ''r'', of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom. It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, ...
*
Van der Waals strain Van der Waals strain is strain resulting from Van der Waals repulsion when two substituents in a molecule approach each other with a distance less than the sum of their Van der Waals radii. Van der Waals strain is also called Van der Waals rep ...
*
Van der Waals surface The Van der Waals surface of a molecule is an abstract representation or model of that molecule, illustrating where, in very rough terms, a surface might reside for the molecule based on the hard cutoffs of Van der Waals radii for individual at ...
* –articles about specific chemicals * Researchers active in this field: ** Donald Levy ** Richard J. Saykally **
Richard Smalley Richard Errett Smalley (June 6, 1943 – October 28, 2005) was an American chemist who was the Gene and Norman Hackerman Professor of Chemistry, Physics, and Astronomy at Rice University. In 1996, along with Robert Curl, also a professor of ...
**
William Klemperer William A. Klemperer (October 6, 1927 – November 5, 2017) was an American chemist who was one of the most influential chemical physicists and molecular spectroscopists in the second half of the 20th century. Klemperer is most widely known fo ...


References

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Further reading

* So far three special issues of ''Chemical Reviews'' have been devoted to vdW molecules: I. Vol. 88(6) (1988). II. Vol. 94(7) (1994). III. Vol. 100(11) (2000). * Early reviews of vdW molecules: G. E. Ewing, ''Accounts of Chemical Research'', Vol. 8, pp. 185-192, (1975): Structure and Properties of Van der Waals molecules. B. L. Blaney and G. E. Ewing, ''Annual Review of Physical Chemistry'', Vol. 27, pp. 553-586 (1976): Van der Waals Molecules. * About VRT spectroscopy: G. A. Blake, ''et al.'', ''Review Scientific Instruments'', Vol. 62, p. 1693, 1701 (1991). H. Linnartz, W.L. Meerts, and M. Havenith, ''Chemical Physics'', Vol. 193, p. 327 (1995). Physical chemistry
Molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and b ...