Excited states of NiH and NiD in the 15 500–19 000 cm−1 region: Rotational analysis with the aid of laser-induced fluorescence spectroscopy

Abstract The first vibrational and rotational analysis is reported for three previously unknown states in NiH in the energy region 15 500 to 19 000 cm −1 . New information about known excited electronic states in this region is also presented. The new states were found in absorption and emission spectra and also in cw laser fluorescence excitation spectra of NiH and NiD. Compared to the group of low-lying states in NiH ( T −1 ) which was reported previously, the density of the vibronic levels from the upper group of states is much higher. However, unambiguous vibrational numbering assignments in the optical spectrum could be obtained based on the observed splittings due to different nickel isotopes and the energy differences between some NiH and NiD bands. The following new labels are given to the upper states to preserve previous lettering and to indicate the Ω value: A 2.5 (formerly A 2 Δ 5 2 ), B 2.5 (formerly B 2 Δ 5 2 ), D 1.5 (formerly 2 Δ 3 2 , E 1.5 (new), F 3.5 (formerly 2 Φ 7 2 ), I 1.5 (new), and G 2.5 (new). From the structure of several bands and the Zeeman patterns of a few lines, a clear relationship is emerging for excited doublet states in NiH arising from the Ni + 3 d 8 4 s 2 F parent. Magnitude of Ω-doublings , consistent vibrational intervals, Δ G 1 2 , and expected spin-orbit interactions link the various substates in this group although a Hund's case (a) picture is not adequate to describe the severely mixed character of these states. There is also some evidence that the A 2.5 state and possibly the E 1.5 state have dominant quartet rather than doublet character.