Potential Energy Function and Vibrational States of the Electronic Ground State of N 4

Three different six-dimensional potential energy functions For the electronic ground state X(2)Sigma(u)(+) of the N-4(+) have been generated by the RCCSD-T method and the B3LYP and B97-1 density functional approaches. The potentials in their analytic forms have been used in variational calculations of the vibrational states (J = 0 and 1). The RCCSD-T rotational B-0 constant of 0.1117 cm(-1) is in excellent agreement with the experimental value of 0.11205 cm(-1). The anharmonic wavenumbers for the fundamentals have been calculated to be nu(1) 2275.6, nu(2) = 390.3, nu(3) = 2239.3 (expt: 2234.5084), nu(4) = 90.7, and nu(5) = 133.8, and the zero-point vibrational energy is 2675.3 (all values in cm(-1)). All large isotope shifts observed in a cold matrix for nu(1) and nu(3) have been very well reproduced. Both density functional approaches yielded good agreement for bending fundamentals but failed to describe accurately the symmetric and antisymmetric stretching vibrations. The dissociation energy, the quadrupole moment and the dipole polarizabilities have been evaluated as well.