Editing Molecular geometry (section)

== Determination ==
The molecular geometry can be determined by various [[spectroscopy|spectroscopic methods]] and [[diffraction]] methods. [[Infrared spectroscopy|IR]], [[Rotational spectroscopy|microwave]] and [[Raman spectroscopy]] can give information about the molecule geometry from the details of the vibrational and rotational absorbance detected by these techniques. [[X-ray crystallography]], [[neutron diffraction]] and [[electron diffraction]] can give molecular structure for crystalline solids based on the distance between nuclei and concentration of electron density. [[Gas electron diffraction]] can be used for small molecules in the gas phase. [[nuclear magnetic resonance|NMR]] and [[Förster resonance energy transfer|FRET]] methods can be used to determine complementary information including relative distances,<!--
References for NMR and FRET distances
--><ref>[http://dwb.unl.edu/Teacher/NSF/C08/C08Links/pps99.cryst.bbk.ac.uk/projects/gmocz/fret.htm FRET description] {{webarchive|url=https://web.archive.org/web/20080918072755/http://dwb.unl.edu/Teacher/NSF/C08/C08Links/pps99.cryst.bbk.ac.uk/projects/gmocz/fret.htm |date=2008-09-18 }}</ref><ref>{{ cite journal| last1=Hillisch| doi=10.1016/S0959-440X(00)00190-1| first1=A| last2=Lorenz| first2=M| last3=Diekmann| first3=S |title=Recent advances in FRET: distance determination in protein–DNA complexes| pmid=11297928 | journal=Current Opinion in Structural Biology| year=2001| volume=11|issue=2 | pages=201–207}}</ref><ref>{{usurped|1=[https://web.archive.org/web/20081014211053/http://www.fretimaging.org/mcnamaraintro.html FRET imaging introduction]}}</ref>
<!-- End References for NMR and FRET distances -->dihedral angles,<!-- References for NMR determination of dihedral angles (through <sup>3</sup>J coupling constants) --><ref>{{usurped|1=[https://web.archive.org/web/20081207031318/http://www.jonathanpmiller.com/Karplus.html obtaining dihedral angles from <sup>3</sup>J coupling constants]}}</ref><ref>[http://www.spectroscopynow.com/FCKeditor/UserFiles/File/specNOW/HTML%20files/General_Karplus_Calculator.htm Another Javascript-like NMR coupling constant to dihedral] {{webarchive|url=https://web.archive.org/web/20051228092336/http://www.spectroscopynow.com/FCKeditor/UserFiles/File/specNOW/HTML%20files/General_Karplus_Calculator.htm |date=2005-12-28 }}</ref>
<!-- End references for NMR determination of dihedral angles (through <sup>3</sup>J coupling constants) -->
angles, and connectivity.  Molecular geometries are best determined at low temperature because at higher temperatures the molecular structure is averaged over more accessible geometries (see next section). Larger molecules often exist in multiple stable geometries ([[conformational isomerism]]) that are close in energy on the [[potential energy surface]].  Geometries can also be computed by [[ab initio quantum chemistry methods]] to high accuracy.  The molecular geometry can be different as a solid, in solution, and as a gas.

The position of each atom is determined by the nature of the [[chemical bond]]s by which it is connected to its neighboring atoms. The molecular geometry can be described by the positions of these atoms in space, evoking [[bond length]]s of two joined atoms, bond angles of three connected atoms, and [[Torsion of a curve|torsion angles]] ([[dihedral angle]]s) of three [[path graph|consecutive]] bonds.