Vacuum ultraviolet spectrum of the iodine molecule

The absorption spectrum of iodine has been photographed in the higher orders of a 10.7 m concave grating spectrograph in the region 1950-1200 &#197; . A number of band systems has been obtained, most of which correspond to Rydberg transitions. The limit of the Rydberg series leading to the <SUP>2</SUP>&#928; <SUB>3/2g</SUB> state of the molecular ion has been recorded and the corresponding ionization potential is found to be 75 814 &#177; 10 cm<SUP>&#8722;1</SUP>. Five series have been found which terminate at this common limit. They represent transitions from the ground state to [&#963; <SUB>g</SUB><SUP>2</SUP>&#960; <SUB>u</SUB><SUP>4</SUP>&#928;<SUB>g</SUB><SUP>32</SUP>&#928;<SUB>3/2g</SUB>]np &#963;<SUB>u</SUB> &#928;<SUB>1u</SUB>, [&#963; <SUB>g</SUB><SUP>2</SUP>&#960; <SUB>u</SUB><SUP>4</SUP>&#960; <SUB>g</SUB><SUP>32</SUP>&#928;<SUB>3/2g</SUB>]np &#960; <SUB>u</SUB> &#931; <SUP>+</SUP> (0<SUB>u</SUB><SUP>+</SUP>), [&#963; <SUB>g</SUB><SUP>2</SUP>&#960; <SUB>u</SUB><SUP>4</SUP>&#960; <SUB>g</SUB><SUP>32</SUP>&#928;<SUB>3/2g</SUB>]nf &#963; <SUB>u</SUB> &#928;<SUB>1u</SUB>, [&#963; <SUB>g</SUB><SUP>2</SUP>&#960; <SUB>u</SUB><SUP>4</SUP>&#960; <SUB>g</SUB><SUP>32</SUP>&#928;<SUB>3/2g</SUB>]nf &#960; <SUB>u</SUB>, &#931; <SUP>+</SUP>(0<SUB>u</SUB><SUP>+</SUP>), and [&#963; <SUB>g</SUB><SUP>2</SUP>&#960; <SUB>u</SUB><SUP>4</SUP>&#960; <SUB>g</SUB><SUP>32</SUP>&#928;<SUB>3/2g</SUB>]nf &#948; <SUB>u</SUB> &#928;<SUB>1u</SUB> states respectively, where n takes the running values 6, 7, 8, - etc. for the first three series and 4, 5, 6, - etc. for the last two series. The series limit of the bands corresponding to the molecules with &#957; " = 1 has been found to be at 75 600 &#177; 10 cm<SUP>&#8722;1</SUP>. The first few members of similar series corresponding to transitions to different states involving the common [&#963; <SUB>g</SUB><SUP>2</SUP>&#960; <SUB>u</SUB><SUP>4</SUP>&#960; <SUB>g</SUB><SUP>32</SUP>&#928;<SUB>1/2g</SUB>] core have been identified and the ionization limit of these series is estimated to be at 80 895 &#177; 50 cm<SUP>&#8722;1</SUP>. Some of the remaining band systems obtained have been found to be very likely due to transitions to the Rydberg states involving molecular ion cores like [&#963; <SUB>g</SUB><SUP>2</SUP>&#960; <SUB>u</SUB> 3&#960; <SUB>g</SUB><SUP>42</SUP>&#928;<SUB>3/2u</SUB>], [&#963; <SUB>g</SUB><SUP>2</SUP>&#960; <SUB>u</SUB><SUP>3</SUP>&#960; <SUB>g</SUB><SUP>42</SUP>&#928;<SUB>1/2u</SUB>], and [&#963; <SUB>g</SUB><SUP>2</SUP>&#960; <SUB>u</SUB><SUP>4</SUP>&#960; <SUB>g</SUB><SUP>2</SUP>&#963; <SUB>u</SUB><SUP>2</SUP>&#931; <SUB>u</SUB><SUP>+</SUP>]. Three of the observed band systems do not appear to involve Rydberg states and their upper levels are very likely the <SUP>1</SUP>&#928;(1<SUB>u</SUB>), <SUP>3</SUP>&#928;(1<SUB>u</SUB>), and <SUP>3</SUP>&#928;(0<SUB>u</SUB><SUP>+</SUP>) states arising from the configuration &#963; <SUB>g</SUB>&#960; <SUB>u</SUB><SUP>3</SUP>&#960; <SUB>g</SUB><SUP>4</SUP>&#963; <SUB>u</SUB><SUP>2</SUP>. The positions of these levels are at 64 956, 62 844, and 61 847 cm<SUP>&#8722;1</SUP>, the corresponding vibrational frequencies being 145, 144, and 109 cm<SUP>&#8722;1</SUP> respectively