Accurate theoretical predictions for carbonyl diazide molecules: A coupled-cluster study of the potential energy surface and thermochemical properties

摘要

Enthalpies of formation (ΔHf°) of syn-syn (C_(2 v)), anti-syn (C_s), and the newly proposed C_2 isomer of carbonyl diazide, OC(N_3)_2, at 298 K have been predicted using CCSD(T) theory in conjunction with a systematic basis set expansion that has been extrapolated to the complete basis set (CBS) limit. The ΔHf° has been calculated via three independent pathways and 'chemical accuracy' has been obtained. The predicted CCSD(T)/CBS values are (kJ mol ~(-1)): syn-syn (C_(2v)), 471.5; anti-syn (C _s), 479.5; C_2, 517.4. These values deviate by 14.5 kJ mol~(-1) compared to prior G4 approximations. CCSD(T) torsional potential energy scan reveals a previously undiscovered conformer of OC(N _3)_2 possessing C_2 symmetry.