Rotationally Resolved Vacuum Ultraviolet Laser Spectra of the 37Cl2 11Sigma+u <-- X1Sigma+g Transition

Rotationally and isotopically resolved single-photon excitation spectra of jet-cooled Cl2 in the wavelength region between 133 and 138 nm were recorded using a tunable vacuum ultraviolet "laser" generated by two-photon resonantly enhanced four-wave difference mixing in Kr gas. The dominant transition (1(1)Sigma+u <-- X1Sigma+g) is well known theoretically and experimentally to involve a double-well excited state potential energy curve formed by a strong homogeneous Rydberg-state/ion-pair state avoided crossing. In this work, single isotopomer spectra were obtained by dispersing and detecting ions produced by (1 + 1') resonance-enhanced multiphoton ionization in a time-of-flight mass spectrometer. In this way, rotational constants were deduced for the first time for many v' levels of the least abundant molecular isotope, 37Cl2, which are both localized in the Rydberg well, and delocalized in the ion-pair portion of the 1-state potential energy curve. Our experimentally derived band origins and B'v values test the practical validity of an analytical 1(1)Sigma+u potential energy function which is a modified version of the one first proposed by J. Wörmer, T. Möller, J. Stapelfeldt, G. Zimmerer, D. Haaks, S. Kampf, J. Le Calvé, and M. C. Castex (1988. Z. Phys. D, 7, 383-395). Copyright 1998 Academic Press.