TiO i^1^{Pi}-a^1^{Delta} system in stellar spectra

The lower state of the band is identified as the a^1^{Delta} v"=0 state, while the upper state is most likely the ^1^{Pi} in its ground vibrational state. The empirical band intensity is derived by comparing the relative strengths of neighbouring bands from the C^3^{Delta}-X^3^{Delta} and B^3^{Pi}^-X^3^{Delta} systems in the experimental cross-section. The band intensity is further validated by synthetic spectrum calculations for the late-type giant 30 Her (M6 III) and comparison with its observed spectrum from the MELCHIORS library.

The i^1^{Pi} (optionally 2^1^{Pi}) electronic state has been predicted by theoretical calculations. While energies of two vibrationally excited states were previously inferred from de-perturbation analyses of the {alpha} system, accurate spectroscopic constants for this electronic state were lacking. The newly identified band is sufficiently strong to affect the flux distribution in the spectra of cool stars.