POTENTIAL-ENERGY FUNCTION AND VIBRATIONAL-STATES OF HN3 AND DN3

Eight different six-dimensional potential energy functions for the ele ctronic ground state of the HN3 have been generated by the CCSD(T) met hod and various density functional approaches. The potentials in their analytic forms have been used in variational calculations of the vibr ational states (J = 0). The calculated anharmonic wavenumbers for the fundamentals agree with the known experimental values to within 7 cm(- 1)(HN3) and 16 cm(-1)(DN,) for the CCSD(T) potential. The best density functional approach (B3LYP) yields fundamentals which are within 10 c m(-1)(HN3) and 44 cm(-1)(DN3), with the exception of the upsilon(2) wh ich is in error by 43 cm(-1)(HN3) and 95 cm(-1)(DN3). Also the experim ental isotope shifts for N-15 substituted species are very well reprod uced for HN3. The barrier to linearity of the HN2 moiety has been calc ulated to be 11 578 cm(-1)(CCSD(T)). Due to the near-linearity of the NNN group, for which a barrier of only 327 cm(-1) has been calculated, the overtones and combination levels of the in-plane upsilon(5) and t he out-of-plane upsilon(6) bending states fall in clusters in higher e xcited states. The vibrational energies for all states up to the NH(ND ) stretching wavenumbers and their assignments are given.