▁and ▁chrom ium . ▁Arg on ▁is ▁only ▁very ▁weak ly ▁bound ▁to ▁t ung sten ▁in ▁Ar W ( CO ) 5 . ▁The ▁Ar − W ▁bond length ▁is ▁predicted ▁to ▁be ▁ 2 . 8 5 2   Å . ▁The ▁same ▁subst ance ▁is ▁produced ▁for ▁a ▁brief ▁time ▁in ▁super crit ical ▁arg on ▁at ▁ 2 1   ° C . ▁For ▁Ar Cr ( CO ) 5 ▁the ▁band ▁maximum ▁is ▁at ▁ 5 3 3   nm ▁( comp ared ▁to ▁ 6 2 4   nm ▁in ▁ne on , ▁and ▁ 5 1 8   nm ▁in ▁k rypt on ). ▁Form ing ▁ 1 8 - elect ron ▁complex es , ▁the ▁shift ▁in ▁spectrum ▁due ▁to ▁different ▁matrices ▁was ▁much ▁smaller , ▁only ▁around ▁ 5   nm . ▁This ▁clearly ▁indicates ▁the ▁formation ▁of ▁a ▁mole c ule ▁using ▁atoms ▁from ▁the ▁matrix . ▁ ▁Other ▁car b ony ls ▁and ▁com pe x ed ▁car b ony ls ▁also ▁have ▁reports ▁of ▁bond ing ▁to ▁arg on . ▁These ▁include ▁Ru ( CO ) 2 ( P Me 3 ) 2 Ar , ▁Ru ( CO ) 2 ( dm pe ) 2 Ar , ▁ η 6 - C 6 H 6 Cr ( CO ) 2 Ar . ▁Ev idence ▁also ▁exists ▁for ▁Ar H M n ( CO ) 4 , ▁Ar CH 3 M n ( CO ) 4 , ▁and ▁fac -( η 2