Extreme ultraviolet laser excitation of isotopic molecular nitrogen: The dipole-allowed spectrum of 15N2 and 14N15N

Abstract

Extreme ultraviolet+ultraviolet (XUV+UV) two-photon ionization spectra of the b 1Πu(v=0–9), c3 1Πu(v=0,1), o 1Πu(v=0,1), c4′ 1Σu+(v=1) and b′ 1Σu+(v=1,3–6) states of 15N2 were recorded with a resolution of 0.3 cm−1 full-width at half-maximum (FWHM). In addition, the b 1Πu(v=1,5–7) states of 14N15N were investigated with the same laser source. Furthermore, using an ultranarrow bandwidth XUV laser [∼250 MHz (∼0.01 cm−1) FWHM], XUV+UV ionization spectra of the b 1Πu(v=0–1,5–7), c3 1Πu(v=0), o 1Πu(v=0), c4′ 1Σu+(v=0), and b′ 1Σu+(v=1) states of 15N2 were recorded in order to better resolve the band-head regions. For 14N15N, ultrahigh resolution spectra of the b 1Πu(v=0–1,5–6), c3 1Πu(v=0), and b′ 1Σu+(v=1) states were recorded. Rotational analyses were performed for each band, revealing perturbations arising from the effects of Rydberg-valence interactions in the 1Πu and 1Σu+ states, and rotational coupling between the 1Πu and 1Σu+ manifolds. Finally, a comprehensive perturbation model, based on the diabatic-potential representation used previously for 14N2, and involving diagonalization of the full interaction matrix for all Rydberg and valence states of 1Σu+ and 1Πu symmetry in the energy window 100 000–110 000 cm−1, was constructed. Term values for 15N2 and 14N15N computed using this model were found to be in good agreement with experiment.