A combined zero electronic kinetic energy spectroscopy and ion-pair dissociation imaging study of the

The fine structure resolved photofragment O(-)((2)P(j)) image from the O(2) ion-pair production at 17.499 eV has been recorded. The branching ratio for producing the low energy spin-orbit O(-)((2)P(3/2)) component to the high energy spin-orbit O(-)((2)P(1/2)) component is 1:0.78 and the optical transitions for them correspond to perpendicular and parallel transitions, respectively. The anisotropy parameters, 1.64 for channel producing O(-)((2)P(1/2)) and -0.35 for O(-)((2)P(3/2)), suggest that the dissociation proceeds via the states with symmetry (3)Sigma(u)(-) and (3)Pi(u), respectively. Although the main mechanisms for the O(2) ion-pair production are the predissociation via the intermediate Rydberg states, the direct dissociation mechanism for the channel producing O(-)((2)P(1/2)) may also be involved.

Rotationally resolved pulsed field ionization and zero electronic kinetic energy photoelectron spectra for the transition F(2) (+)(X (2)Pi(g))<--F(2)(X (1)Sigma(g) (+)) have been recorded using the extreme ultraviolet coherence radiation. The vibrational energy spacings, rotational constants, and spin orbit coupling constants for the first three vibrational states of F(2) (+)(X (2)Pi(g)) have been determined accurately. The first adiabatic ionization potential (IP) of F(2) is determined as IP(F(2))=126 585.7+/-0.5 cm(-1). To determine the threshold E(tipp) for ion-pair production of F(2), the images of F(-)((1)S(0)) in the velocity mapping conditions have also been recorded at the photon energy of 126 751 cm(-1). Taking the Stark effect into account, the E(tipp) is determined as E(tipp)(F(2))=126 045+/-8 cm(-1) (15.628+/-0.001 eV). By combing the IP(F(2)) and the E(tipp)(F(2)) determined in this work and together with the reported ionization potential and electronic affinity of the F atom, the bond dissociation energies of F(2) and F(2) (+) are determined as D(0)(F(2))=1.606+/-0.001 eV and D(0)(F(2) (+))=3.334+/-0.001 eV, respectively.

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(+)((1)D(2)) from those of Cl(+)((3)P(j)), the threshold for ion-pair (E(tipp)) production, Cl(+)((1)D(2))+Cl(-)((1)S(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.

The ion-pair dissociation dynamics of Cl2 -->(XUV) Cl(-)((1)S0) + Cl(+)((3P(2,1,0)) in the range 12.41-12.74 eV have been studied employing coherent extreme ultraviolet (XUV) radiation and the velocity map imaging) method. The ion-pair yield spectrum has been measured, and 72 velocity map images of Cl(-)((1)S0) have been recorded for the peaks in the spectrum. From the images, the branching ratios among the three spin-orbit components Cl(+)((3)P2), Cl(+)((3)P1) and Cl(+)((3)P0) and their corresponding anisotropic parameters beta have been determined. The ion-pair dissociation mechanism is explained by predissociation of Rydberg states converging to ion-core Cl2(+)(A(2)Pi(u)). The Cl(-)((1)S0) ion-pair yield spectrum has been assigned based on the symmetric properties of Rydberg states determined in the imaging experiments. The parallel and perpendicular transitions correspond to the excitation to two major Rydberg series, [A(2)Pi(u)]3d pi(g), (1)Sigma(u)(+) and [A(2)Pi(u)]5s sigma(g), (1)Pi(u), respectively. For the production of Cl(+)((3)P0), it is found that all of them are from parallel transitions. But for Cl(+)((3)P1), most of them are from perpendicular transitions. The production of Cl(+)((3)P2) is the major channel in this energy region, and they come from both parallel and perpendicular transitions. It is found that for most of the predissociations the projection of the total electronic angular momentum on the molecular axis (Omega) is conserved. The ion-pair dissociation may be regarded as a probe for the symmetric properties of Rydberg states.