▁hel ium ▁atom ▁clusters . ▁The ▁existence ▁of ▁the ▁mole c ule ▁was ▁proven ▁by ▁matter ▁wave ▁diff raction ▁through ▁a ▁diff raction ▁gr ating . ▁Properties ▁of ▁the ▁mole cules ▁can ▁be ▁discovered ▁by ▁C oul omb ▁explos ion ▁imag ing . ▁In ▁this ▁process , ▁a ▁las er ▁ion izes ▁all ▁three ▁atoms ▁simultaneously , ▁which ▁then ▁fly ▁away ▁from ▁each ▁other ▁due ▁to ▁electro static ▁rep ulsion ▁and ▁are ▁detected . ▁ ▁The ▁hel ium ▁tr imer ▁is ▁large , ▁being ▁more ▁than ▁ 1 0 0   Å , ▁which ▁is ▁even ▁larger ▁than ▁the ▁hel ium ▁dim er . ▁The ▁atoms ▁are ▁not ▁arranged ▁in ▁an ▁equ il ater al ▁triangle , ▁but ▁instead ▁form ▁random ▁sh aped ▁tri angles . ▁ ▁Inter atomic ▁C oul omb ic ▁decay ▁can ▁occur ▁when ▁one ▁atom ▁is ▁ion ised ▁and ▁excited . ▁ ▁It ▁can ▁transfer ▁energy ▁to ▁another ▁atom ▁in ▁the ▁tr imer , ▁even ▁though ▁they ▁are ▁separated . ▁However ▁this ▁is ▁much ▁more ▁likely ▁to ▁occur ▁when ▁the ▁atoms ▁are ▁close ▁together , ▁and ▁so ▁the ▁inter atomic ▁distances ▁measured ▁by ▁this ▁vary ▁with ▁half ▁full ▁height ▁from ▁ 3 . 3 ▁to ▁ 1 2   Å . ▁The ▁predicted ▁mean ▁distance ▁for ▁Inter atomic ▁C oul omb ic ▁decay ▁in ▁ 4 He 3 ▁is ▁ 1 0 . 4   Å . ▁For ▁ 3 He 4 He 2 ▁this ▁distance ▁is ▁even ▁larger ▁at ▁ 2 0 . 5   Å . ▁