C. Leonard et al., Potential energy function and vibrational states of the electronic ground state of N-4(+), J PHYS CH A, 103(12), 1999, pp. 1846-1852
Three different six-dimensional potential energy functions For the electron
ic ground state X(2)Sigma(u)(+) of the N-4(+) have been generated by the RC
CSD-T method and the B3LYP and B97-1 density functional approaches. The pot
entials in their analytic forms have been used in variational calculations
of the vibrational states (J = 0 and 1). The RCCSD-T rotational B-0 constan
t 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: 2234.50
84), 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 c
old 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 vi
brations. The dissociation energy, the quadrupole moment and the dipole pol
arizabilities have been evaluated as well.