Editing Rotational spectroscopy (section)

==Applications==
Rotational spectroscopy has primarily been used to investigate fundamental aspects of molecular physics. It is a uniquely precise tool for the determination of molecular structure in gas-phase molecules.  It can be used to establish barriers to internal rotation such as that associated with the rotation of the {{chem|CH|3}} group relative to the {{chem|C|6|H|4|Cl}} group in [[chlorotoluene]] ({{chem|C|7|H|7|Cl}}).<ref>{{cite journal|last=Nair|first=K.P.R.|author2=Demaison, J.|author3=Wlodarczak, G.|author4=Merke, I.|title=Millimeterwave rotational spectrum and internal rotation in o-chlorotoluene|journal=Journal of Molecular Spectroscopy|date=236|volume=237|issue=2|pages=137–142|doi=10.1016/j.jms.2006.03.011|bibcode = 2006JMoSp.237..137N }}</ref> When fine or hyperfine structure can be observed, the technique also provides information on the electronic structures of molecules. Much of current understanding of the nature of weak molecular interactions such as [[Van der Waals force|van der Waals]], [[Hydrogen bond|hydrogen]] and [[Halogen bond|halogen]] bonds has been established through rotational spectroscopy. In connection with radio astronomy, the technique has a key role in exploration of the chemical composition of the interstellar medium. Microwave transitions are measured in the laboratory and matched
to emissions from the interstellar medium using a [[radio telescope]]. {{chem|link=ammonia|NH|3}} was the first stable [[polyatomic]] molecule to be identified in the interstellar medium.<ref>{{cite journal|last=Cheung|first=A.C.|author2=Rank, D.M. |author3=Townes, C.H. |author4= Thornton, D.D. |author5= Welch, W.J. |name-list-style= amp |title=Detection of {{chem|NH|3}} molecules in the interstellar medium by their microwave emission spectra|journal=Physical Review Letters|date=1968|volume=21|pages=1701–5|doi=10.1103/PhysRevLett.21.1701|bibcode = 1968PhRvL..21.1701C|issue=25 }}</ref> The measurement of [[chlorine monoxide]]<ref>{{cite journal|last=Ricaud|first=P.|author2=Baron, P|author3= de La Noë, J.|title=Quality assessment of ground-based microwave measurements of chlorine monoxide, ozone, and nitrogen dioxide from the NDSC radiometer at the Plateau de Bure|journal=Ann. Geophys.|date=2004|volume=22|issue=6|pages=1903–15|doi=10.5194/angeo-22-1903-2004|bibcode = 2004AnGeo..22.1903R |doi-access=free}}</ref>  is important for [[atmospheric chemistry]]. Current projects in astrochemistry involve both laboratory microwave spectroscopy and observations made using modern radiotelescopes such as the [[Atacama Large Millimeter Array|Atacama Large Millimeter/submillimeter Array]] (ALMA).<ref>{{cite web|title=Astrochemistry in Virginia|url=http://www.virginia.edu/ccu/molecspectroscopy.html|access-date=2 December 2012}}</ref>