In 1910 R.J.Strutt (Lord Rayleigh) discovered that an electrical discharge in nitrogen gas produced "active nitrogen", an allotrope considered to be monatomic. The "whirling cloud of brilliant yellow light" produced by his apparatus reacted with quicksilver to produce explosive mercury nitride.

From Modern Inorganic Chemistry, J.W.Mellor 1934 --

From A Text-Book of Inorganic Chemistry, J.R.Partington 1946 --