The band systems ending on the 1 s σ2 s σ 1 Ʃ g ( 1 X g ) state of H 2 —Part I

Abstract

It is now well established that the electronic states of the band systems of H 2 have a close analogy to those of atomic helium and consist of a set of singlet states and a set of triplet states. There are no known combinations between singlet and triplet states. The ground level of H 2 is the v = 0, K = 0 level of the even state 1 s σ 1 s σ 1 Ʃ g . The possible states with one electron excited to principal quantum number 2 are 1 s σ 2 s σ 1 Ʃ g , 1 s σ 2 p σ 1 Ʃ u , 1 s σ 2 pπ 1 II u , 1 s σ 2 s σ 3 Ʃ g , 1 s σ 2 p σ 3 Ʃ g and 1 s σ 2 pπ 3 II u Of these the only ones which can go down to the ground state are 1 s σ 2 p σ 1 Ʃ u and 1 s σ 2 pπ σ 1 Ʃ u on account of the triplet ↔ singlet and odd ↔ odd and even ↔ even prohibitions. The bands with these transitions are well known and understood both in emission and absorption. A large number of emission band systems which go down to the states 1 s σ 2 p σ 1 Ʃ u and 1 s σ2 pπ σ 1 II u from higher even states have been found and analysed so that we now have quite discovered, and most of those involving the v = 1 level, which he has greatly extended, I am indebted to a private communication from Professor Dieke. Incidentally the success of this method of locating the position of 1 s σ3 pπ 1 II u is to some extent also a confirmation of my identification of 3 1 O as 1 s σ 3 s σ 1 Ʃ g .