Vacuum ultraviolet photoexcitation and photofragment spectroscopic studies of ¹⁴N¹⁵N between 109000 and 117500 cm⁻¹

In this study, we employed a newly built time-slice velocity-map ion imaging setup, equipped with two tunable vacuum ultraviolet (VUV) laser sources, to obtain the first comprehensive high-resolution photoexcitation and photofragment excitation spectra of ¹⁴N¹⁵N in the VUV photon energy range 109 000–117 500 cm⁻¹. The spectroscopic simulation program PGOPHER was used to analyze the rotationally resolved spectra. Band origins, rotational constants, and isotope shifts compared with those of ¹⁴N₂ have been obtained for 31 electric-dipole-allowed vibrational states of ¹⁴N¹⁵N in the aforementioned energy range. These spectroscopic parameters are found to depend on the vibrational quantum number irregularly. Systematic perturbations of the rotational transition energies and predissociation rates within individual absorption bands have also been observed. These are proved to be caused by the strong homogeneous interactions between the valence b′¹Σ_u⁺ state and the Rydberg $cn′$ ¹Σ_u⁺ states, and between the valence b¹Π_u states and the Rydberg o₃¹Π_u states. Heterogeneous interactions between the Rydberg c_n¹Π_u states and $cn′$¹Σ_u⁺ states also play an important role.