▁mole cular ▁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 ▁b onds ▁by ▁which ▁it ▁is ▁connected ▁to ▁its ▁neighbor ing ▁atoms . ▁The ▁mole cular ▁geometry ▁can ▁be ▁described ▁by ▁the ▁positions ▁of ▁these ▁atoms ▁in ▁space , ▁ev oking ▁bond ▁lengths ▁of ▁two ▁joined ▁atoms , ▁bond ▁angles ▁of ▁three ▁connected ▁atoms , ▁and ▁t ors ion ▁angles ▁( d ih ed ral ▁angles ) ▁of ▁three ▁consecutive ▁b onds . ▁ ▁The ▁influence ▁of ▁thermal ▁exc itation ▁ ▁Since ▁the ▁mot ions ▁of ▁the ▁atoms ▁in ▁a ▁mole c ule ▁are ▁determined ▁by ▁quantum ▁mechan ics , ▁one ▁must ▁define ▁" m otion " ▁in ▁a ▁quantum ▁mechanical ▁way . ▁The ▁overall ▁( external ) ▁quantum ▁mechanical ▁mot ions ▁translation ▁and ▁rotation ▁hardly ▁change ▁the ▁geometry ▁of ▁the ▁mole c ule . ▁( To ▁some ▁extent ▁rotation ▁influ ences ▁the ▁geometry ▁via ▁Cor i olis ▁forces ▁and ▁cent rif ug al ▁dist ort ion , ▁but ▁this ▁is ▁neg lig ible ▁for ▁the ▁present ▁discussion .) ▁In ▁addition ▁to ▁translation ▁and ▁rotation , ▁a ▁third ▁type ▁of ▁motion ▁is ▁mole cular ▁v ibration , ▁which ▁corresponds ▁to ▁internal ▁mot ions ▁of ▁the ▁atoms ▁such ▁as ▁bond ▁stretch ing ▁and ▁bond ▁angle ▁variation . ▁The ▁mole cular ▁v ibr ations ▁are ▁harm onic ▁( at ▁least ▁to ▁good ▁approximation ), ▁and ▁the ▁atoms ▁oscill ate ▁about ▁their ▁equilibrium ▁positions