Structures and Energetics of NI 3 and N 2 I 4 .

We have applied new methods for performing coupled-cluster calculations to small molecules containing iodine atoms; specifically, NI3 and N2 I4 . Because NI3 is known to be very reactive, attempts to measure its thermodynamic properties have been challenging at best. To date, N2 I4 has not been isolated, and our results suggest that its isolation will be just as challenging. We find that the ΔHf (NI3 )=+307.7 kJ mol-1 and ΔHf (N2 I4 )=+551.6 kJ mol-1 , confirming that they are unstable with respect to their decomposition products N2 and I2 .