Vibrational structure, spin-orbit splitting, and bond dissociation energy of Cl2+(X2Πg) studied by zero kinetic energy photoelectron spectroscopy and ion-pair formation imaging method

The isotopomer-resolved vibrational and spin-orbit energy structures of Cl-2(+)(X (2)Pi(g)) have been studied by one-photon zero kinetic energy photoelectron spectroscopy. The spin-orbit energy splitting for the ground vibrational state is determined as 717.7 +/- 1.5 cm(-1), which greatly improves on the accuracy of the previously reported data. This value is found to be in good agreement with the ab initio quantum chemical calculation taking account of the inner shell electron correlation. The first adiabatic ionization energy (IE) of Cl-2 is determined as 92 645.9 +/- 1.0 cm(-1). Using the ion-pair formation imaging method to discriminate signals of Cl+(D-1(2)) from those of Cl+(P-3(j)), the threshold for ion-pair (E-tipp) production, Cl+(D-1(2))+Cl-(S-1(0))<- Cl-2(X (1)Sigma(+)(g)), is determined as 107 096(-2)(+8) cm(-1). By using the determined IE and E-tipp for Cl-2 and also the reported IE and electronic affinity for chlorine atom, the bond dissociation energies of Cl-2(X (1)Sigma(+)(g)) and Cl-2(+)(X (2)Pi(g)) have been determined as 19 990(-2)(+8) and 31 935.1(-2)(+8), respectively.