A spectroscopic investigation of the lowest electronic states of the I₂⁺ cation as a candidate for detecting the time variation of fundamental constants

The four lowest Ω substates (X²Π_3/2,g, X²Π_1/2,g, A²Π_3/2,u and A²Π_1/2,u) of the I₂⁺ cation have been studied by high-precision ab initio calculations in comparison with experimental high-resolution absorption spectra. The potential energy curves were calculated using the multi-reference configuration interaction (MRCI) method and Dirac method, respectively. Rovibrational levels of these electronic states were derived by solving the radial Schrödinger rovibrational equation. Molecular constants were obtained in fitting energy levels to a spectroscopic model. Using the fit spectroscopic constants and newly calculated transition dipole moment matrix elements, line strengths of vibronic bands in the A²Π_3/2,u- X²Π_3/2,g system, as well as Einstein A coefficients for 45 of these bands with ν′ = 11–19 and ν′′ = 1–5, have been derived. The Einstein A coefficients were used to compute radiative lifetimes of the ν′ = 11–19 vibrational levels of the A²Π_3/2,u state. Enhancement factors for detecting the variation of the fine-structure constant (α) and the proton-to-electron mass ratio(µ) using transitions between nearly degenerate rovibronic levels of these low-lying states have been calculated.