▁der ▁Wa als ▁mole c ule ▁of ▁Ar H , ▁the ▁bond ▁length ▁is ▁calculated ▁to ▁be ▁about ▁ 3 . 6   Å ▁and ▁the ▁dis soci ation ▁energy ▁calculated ▁to ▁be ▁ 0 . 4 0 4   k J / m ol ▁( 3 3 . 8   cm − 1 ). ▁The ▁bond ▁length ▁in ▁Ar H * ▁is ▁calculated ▁as ▁ 1 . 3 0 2   Å . ▁ ▁The ▁spectrum ▁of ▁arg on ▁mon oh yd ride , ▁both ▁Ar H * ▁and ▁Ar D *, ▁has ▁been ▁studied . ▁The ▁lowest ▁bound ▁state ▁is ▁term ed ▁A 2 Σ + ▁or ▁ 5 s . ▁Another ▁low ▁lying ▁state ▁is ▁known ▁as ▁ 4 p , ▁made ▁up ▁of ▁C 2 Σ + ▁and ▁B 2 π ▁states . ▁Each ▁transition ▁to ▁or ▁from ▁higher ▁level ▁states ▁corresponds ▁to ▁a ▁band . ▁Kn own ▁bands ▁are ▁ 3 p   →   5 s , ▁ 4 p   →   5 s , ▁ 5 p   →   5 s ▁( band ▁origin ▁), ▁ 6 p   →   5 s ▁( band ▁origin ▁) ▁ 3 d σ   →   4 p , ▁ 3 d π   →   4 p ▁( 6 9 0 0   cm − 1 ), ▁ 3 d δ   →   4 p ▁( 8 2 0 0 – 8 8 0 0   cm − 1 ), ▁ 4 d σ