A semiempirical analysis is performed of data on electronic vibration-rotation (EVR) levels of mutually perturbed i³Π^- and j³Δ^- states and relative spontaneous emission probabilities for transitions from these states to the c³Π_u state in H₂ ^g and D₂ molecules. The expansion coefficients for the perturbed wave functions in the Born-Oppenheimer basis for the H₂, HD, and D₂ molecules are obtained. Analysis of the isotope effect in the line strength ratios for various branches of the i³Π_g ^-→c³Π_u and j³Δ_g→c³Π_u transitions showed that: (1) experimental data (76 values) are adequately described in the framework of the proposed nonadiabatic model with the help of a single variable parameter, namely, the ratio of the electronic dipole moments for these transitions, M_jc/M_ic = -1.35±0.05; (2) the dependence of the above parameter on the internuclear distance r can be neglected in the range r = 1.5-3.0 a.u.; (3) the electron-rotation coupling of the b³Σ_u ⁺ and c³Π_u ⁺ states is not essential at 10% accuracy of the relative line strength measurements. The obtained M_jc/M_ic value agrees well with that determined by laser photofragmentation spectroscopy and differs by 20-30% from the ab initio value.