Argon ion and dye laser induced MgO B1Σ +- X1Σ + and B1Σ +- A1Π photoluminescence spectra : Analysis of a3Π i ∼ X1Σ + perturbations

Abstract

We have experimentally demonstrated that the electronic ground state of MgO is X 1Σ +. The lowest energy excited state was shown to be a 3Π i , for which the following constants were determined (1σ uncertainty in parentheses): T e 2623 (7) cm −1 ω e 648 (5) ω ex e 3.9 (9) B e 0.5022 (13) α e 0.0042 (8) (Pekeris' relation) A −64 (1) The a 3Π i state was observed and characterized from its perturbations of the X 1Σ + ( v X > 2) levels. These perturbations were detected in the photoluminescence from the B 1Σ + state induced by the 476.5-, 496.5-, and 514.5-nm lines of an argon ion laser. The three laser lines were shown to coincide with a total of eight strong and assignable molecular lines belonging to the B 1Σ + - X 1Σ + system of the three isotopic species 24Mg 16O, 25Mg 16O, and 26Mg 16O. The 496.5-nm line excited the less abundant 26Mg 16O species almost exclusively. Rotationally resolved photoluminescence from eight B 1Σ + ( v B , J B ) levels was observed into vibronic levels X 1Σ + ( v X = 0–7) and A 1Π ( v A = 0–8). X 1Σ + ∼ a 3Π i perturbations appeared as level shifts often accompanied by extra transitions into levels of dominants a 3Π i character; a total of 20 extra lines were assigned. A 1Π ∼ X 1Σ + perturbations were also observed, and six extra lines were assigned. Measurement of the relative intensities of B 1Σ + - A 1Π and B 1Σ + - X 1Σ + photoluminescence originating simultaneously from a single ( v B , J B ) level permitted determination of the transition moment ratio T e 2623 (7) cm −1 ω e 648 (5) ω eX e 3.9 (9) β e 0.5022 (13) α e 0.0042 (8) (Pekeris' relation) A −64 (1) The electronically excited A 1Π state was present in our Mg + N 2O flame in sufficient concentration to record the MgO B 1Σ + ← A 1Π excitation spectrum using a cw Rhodamine 6G dye laser. This observation raises the possibility of direct population monitoring of other electronically excited species in flames.