Near infrared spectroscopy of NiF

Four new electronic transitions of NiF, recorded by high-resolution Fourier transform spectroscopy, have been located in the near infrared spectral region. The three new upper electronic states are labeled as [12.5]2Δ5/2, [9.9]Ω = 1/2 and [6.3]2Π3/2. In addition, the first excited state located at 251 cm−1 above the ground X2Π1/2 state has been revisited on the basis of the work carried out by Kopp and Hougen [Can. J. Phys. 45 (1967) 2581-2596], who showed that an Ω = 1/2 state can be described either as a 2Σ state or a 2Π1/2 state. For NiF, both descriptions of this state have large fine-structure constants with γ = −0.9599 cm−1 for a 2Σ description and p = −0.7399 cm−1 for a 2Π1/2 description consist with a state of mixed character. If this low-lying state is considered to be a [0.25]2Π1/2 state rather than a [0.25]2Σ state (as proposed up to now), then the experimental pattern of the low-lying electronic states of NiF is similar to those of the related molecules NiH and NiCl.