THE A2-PI-X2-SIGMA+ SYSTEM OF MGCL - EVIDENCE FOR PREDISSOCIATION IN THE A 2-PI STATE OF MGCL

The A 2Π-X2Σ+ system of MgCl has been reinvestigated. Laser excitation spectra of MgCl formed in a Broida oven, from the reaction Mg (3P) +R-Cl (R = Cl, CH2Cl, CHCl2, CCl3, C2H4Cl, C4H8Cl, C6H5, and CH2C6H5) have been recorded under medium resolution. The sudden cut-off of the vibrational structure (at VA{succeeds above single-line equals sign}7), in all cases, is interpreted as arising from an avoided crossing between the ... (3π)4 (4π)1 regular A 2II state and the ... (3π)3 repulsive and inverted (D)2Π state. The strong interaction between the two 2Π states results in a predissociation of the A state and would explain the observed anomalous r-dependence of ΔGv +1 2 and Avso. An overall fit of all the presently available spectroscopic data provided a consistent set of vibrational and rotational constants for the A and X states of MgCl. © 1990.