The CCSD(T) method has been used to compute a highly accurate quartic force field and fundamental frequencies for all N-14 and N-15 isotopomers of the high energy density material TdN4. The computed fundamental frequencies show beyond doubt that the bands observed in a matrix isolation experiment by Radziszewski and coworkers [Chem. Phys. Lett. 328 (2000) 227] are not due to different isotopomers of TdN4. The most sophisticated thermochemical calculations to date yield a 2N(2) --> N-4 heat of reaction of 182.22 +/- 0.5 kcal/mol at 0 K (180.64 +/-0.5 at 298 K). It is hoped that the data reported herein will aid in the ultimate detection of TdN4. (C) 2002 Published by Elsevier Science B.V.