The structures and vibrations of several linear centrosymmetrical isomers o
f C5N2 were investigated by DFT. Tripler ((3)Sigma(g)(-)) and open-shell si
nglet ((1)Sigma(g)(-)) states of NCCCCCN were found to have the lowest ener
gies. The calculated frequencies and isotope shifts are in excellent agreem
ent with the experimental results of prominent vibrational bands observed i
n rare-gas matrices [Chem, Phys. 184 (1994) 233], thus confirming the concl
usion that linear centrosymmetrical NCCCCCN was generated in rare-gas matri
ces. However, the calculated results are not in reasonable agreement with t
he observed frequencies of weaker bands, suggesting these weaker bands orig
inate from something else. (C) 1999 Elsevier Science B.V. All rights reserv
ed.