▁short ▁and ▁two ▁longer ▁Ti - Ar ▁b onds . ▁Ti + Ar 4 ▁is ▁a ▁dist orted ▁t etra hed ron , ▁with ▁one ▁longer ▁Ti - Ar ▁bond . ▁Ti + Ar 5 ▁is ▁an ▁asym met rical ▁trig onal ▁b ip y ram id ▁shape ▁with ▁one ▁bond ▁shorter . ▁For ▁clusters ▁with ▁seven ▁or ▁more ▁arg on ▁atoms , ▁the ▁structure ▁contains ▁a ▁Ti + Ar 6 ▁oct ah ed ton ▁with ▁tri angular ▁faces ▁cap ed ▁by ▁more ▁arg on ▁atoms . ▁ ▁Cu + Ar 2 ▁is ▁predicted ▁to ▁be ▁linear . ▁Cu + Ar 3 ▁is ▁predicted ▁to ▁be ▁plan ar ▁T ▁sh aped ▁with ▁an ▁Ar - C u - Ar ▁angle ▁of ▁ 9 3 ° . ▁Cu + Ar 4 ▁is ▁predicted ▁to ▁be ▁rh omb ic ▁plan ar ▁( not ▁square ▁or ▁t etra hed ral ). ▁For ▁alk ali ▁and ▁al kal ine ▁earth ▁met als ▁the ▁M + Ar 4 ▁cluster ▁is ▁t etra hed ral . ▁Cu + Ar 5 ▁is ▁predicted ▁to ▁have ▁a ▁rh omb ic ▁py ram id ▁shape . ▁Cu + Ar 6 ▁has ▁a ▁fl atten ed ▁oct ah ed ral ▁shape . ▁Cu + Ar 7 ▁is ▁much ▁less ▁stable , ▁and ▁the ▁sevent h ▁arg on ▁atom ▁is ▁outside ▁an ▁inner ▁shell ▁of ▁six ▁arg on ▁atoms . ▁ ▁This ▁is ▁called ▁c apped ▁oct ah ed ral . ▁A ▁complete ▁second ▁shell ▁of ▁arg on ▁atoms ▁yields ▁Cu + Ar 3