Spectroscopy of nickel chloride: Identification of the [15.0] Π3/2 and [15.0] Δ5/2 states

Vibrational bands belonging to the 15.0] ²Δ_5/2-A²Δ_5/2, 15.0] ²Δ_5/2-X²Π_3/2, and 15.0] ²Π_3/2-X²Π_3/2 electronic transitions of NiCl have been observed in the 14 000-16 000 cm⁻¹ region. The 15.0] ²Δ_5/2 and 15.0] ²Π_3/2 states are identified for the first time. The observed bands have been recorded at high spectral resolution using several techniques, which include intracavity laser spectroscopy (ILS), Fourier transform emission spectroscopy (FTS), and laser induced fluorescence (LIF) spectroscopy. For the ILS absorption spectra, NiCl molecules were produced in a nickel hollow cathode operated with a small amount of CCl₄. For the FTS emission spectra, excited NiCl molecules were produced in a King-type carbon tube furnace loaded with NiCl₂ and heated to 1600 °C. In the LIF work, NiCl molecules were produced by reacting laser-ablated nickel with PCl₃ seeded in argon. Detailed analysis of rotational transition lines indicates that the observed 15.0] ²Δ_5/2 and 15.0] ²Π_3/2 states are only separated by 10 cm⁻¹ and are interacting with each other. Molecular constants for these newly observed electronic states are reported.