ally ▁populated ▁with ▁rising ▁temper atures . ▁Typ ical ▁rot ational ▁exc itation ▁energ ies ▁are ▁on ▁the ▁order ▁of ▁a ▁few ▁cm − 1 . ▁The ▁results ▁of ▁many ▁spect ro scop ic ▁experiments ▁are ▁bro aden ed ▁because ▁they ▁involve ▁an ▁aver aging ▁over ▁rot ational ▁states . ▁It ▁is ▁often ▁difficult ▁to ▁extract ▁geomet ries ▁from ▁spect ra ▁at ▁high ▁temper atures , ▁because ▁the ▁number ▁of ▁rot ational ▁states ▁prob ed ▁in ▁the ▁experimental ▁aver aging ▁increases ▁with ▁increasing ▁temperature . ▁ ▁Thus , ▁many ▁spect ro scop ic ▁observations ▁can ▁only ▁be ▁expected ▁to ▁yield ▁reliable ▁mole cular ▁geomet ries ▁at ▁temper atures ▁close ▁to ▁absolute ▁zero , ▁because ▁at ▁higher ▁temper atures ▁too ▁many ▁higher ▁rot ational ▁states ▁are ▁therm ally ▁populated . ▁ ▁Bond ing ▁▁ ▁M ole cules , ▁by ▁definition , ▁are ▁most ▁often ▁held ▁together ▁with ▁c oval ent ▁b onds ▁involving ▁single , ▁double , ▁and / or ▁triple ▁b onds , ▁where ▁a ▁" b ond " ▁is ▁a ▁shared ▁pair ▁of ▁electrons ▁( the ▁other ▁method ▁of ▁bond ing ▁between ▁atoms ▁is ▁called ▁ion ic ▁bond ing ▁and ▁involves ▁a ▁positive ▁c ation ▁and ▁a ▁negative ▁an ion ). ▁ ▁M ole cular ▁geomet ries ▁can ▁be ▁specified ▁in ▁terms ▁of ▁bond ▁lengths , ▁bond ▁angles ▁and ▁t ors ional ▁angles . ▁The ▁bond ▁length ▁is ▁defined ▁to ▁be ▁the ▁average ▁distance ▁between ▁the ▁nuc lei ▁of ▁two ▁atoms ▁bond ed ▁together ▁in ▁any ▁given ▁mole c ule . ▁A