E 0g+→A 1u and E 0g+→B″ 1u laser-induced fluorescence in molecular iodine recorded by Fourier-transform spectroscopy Original Research Article

The E 0g+→A 1u(3Πu) and E 0g+→B″ 1u(1Πu) fluorescence has been recorded at moderate resolution (0.150 cm−1) in the range 28600–31600 cm−1, using the direct optical–optical double resonance: E 0g+←B 0u+←X 0g+. Both the 1u states observed in fluorescence correlate with ground-state I atoms. The Ω-type doubling observed in these states is interpreted in terms of their interactions with the two 0u− states dissociating at the same limit. This is the first rotational analysis of the weakly bound B″ 1u state. The equilibrium spectroscopic constants are Te=12344.804(40) cm−1, ωe=19.83(3) cm−1, Be=0.014607(11) cm−1 and re=4.265 Å. The last observed vibrational level is v″=20 which is located 0.978 cm−1 below the dissociation limit. The parameters describing the long-range part of the potential curve are De (B″ 1u)=202.53(4) cm−1, C5=−0.49(28)×105 cm−1 Å5, C6=1.00(33)×106 cm−1 Å6, C8=0.40(6)×108 cm−1 Å8. The last bound vibrational level is v=23−1+0. In addition a self-induced electronic collision transfer E 0+g(v′,J′)→coll.D 0+u(vt,Jt) is observed with the strong propensity rule Jt=J′±1 and a vibrational propensity v′→vt governed by the proximity of the resonance between the energy loss in D 0+u(vt,Jt) and the energy separation (J″−Jt″∼0) of rovibrational levels of the X 0+g(v″,J″) partner in the collision.