Potential energy function and vibrational states of HN3 and DN3

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Abstract
Eight different six-dimensional potential energy functions for the electronic ground state of the HN3 have been generated by the CCSD(T) method and various density functional approaches. The potentials in their analytic forms have been used in variational calculations of the vibrational states (J = 0). The calculated anharmonic wavenumbers for the fundamentals agree with the known experimental values to within 7cm-1(HN3) and 16cm-1(DN3) for the CCSD(T) potential. The best density functional approach (B3LYP) yields fundamentals which are within 10cm-1(HN3) and 44cm-1(DN3), with the exception of the ν2 which is in error by 43cm-1(HN3) and 95cm-1(DN3). Also the experimental isotope shifts for 15N substituted species are very well reproduced for HN3. The barrier to linearity of the HN2 moiety has been calculated to be 11578cm-1(CCSD(T)). Due to the near-linearity of the NNN group, for which a barrier of only 327cm-1 has been calculated, the overtones and combination levels of the in-plane ν5 and the out-of-plane ν6 bending states fall in clusters in higher excited states. The vibrational energies for all states up to the NH(ND) stretching wavenumbers and their assignments are given.