Nitrogen triiodide detonating (3 of 4) as a balloon is dropped onto it. Nitrogen triiodide (NI3) is an extremely sensitive contact explosive. Its sensitivity is due to the immense strain in the molecule, in which three large iodine atoms are bound to a small nitrogen. The slightest touch can cause the breakdown of the NI3 molecules, leading to the production of nitrogen gas and a cloud of iodine vapour. This is a still frame taken from footage filmed at 2000 frames per second.