Probing the 1(2)Sigma(+)(u) cation state by low-energy dissociative ionization of Na-2

We have measured highly resolved time-of-flight spectra and concomitant ang ular distributions of slow Na+ ions produced by near-threshold dissociative ionization of Na,. Using double-resonance excitation via the A(1)Sigma(u)( +) state, Na, molecules are promoted to rotational levels J = 14 or 16 and vibrational levels between upsilon = 50 and 69 of the 4 (1)Sigma(g)(+) stat e. Then, a third photon-from the second of two tunable dye lasers employed- causes the transition into the double continuum associated with the 1(2)Sig ma(u)(+) potential of the Na-2(+) cation. A detailed Monte Carlo simulation is employed to study the dynamics of this dissociative ionization process in detail. Based on this approach, we were able to subject recent calculati ons of this 1(2)Sigma(u)(+) potential to experimental scrutiny. We find our data to be compatible with a zero-energy crossing near 8.8 Angstrom and a well depth of about 70 cm(-1), which agrees with most of the published calc ulations. Angular distributions for the vibrational level upsilon = 60 are also reproduced well using the same potential parameters and an anisotropy parameter beta = 2 modified by a semiclassical argument to account for pare nt molecule rotation. [S1050-2947(99)07708-2].