Using the technique of flash photolysis with the compound diazomethane, 
Gerhard Herzberg and Jack Shoosmith 
were the first to 
produce and spectroscopically characterize the methylene molecule. In their work they obtained
the ultraviolet spectrum of gas phase methylene at around 141.5 nm. Their
analysis of the spectrum lead them to the conclusion that the ground electronic state was an 
electronic triplet state and that the equilibrium structure was either linear, or else it had 
a large bond angle of about 140°. It turns out that the latter is correct. The reactions of methylene were also studied around 1960, by infrared spectroscopy in frozen gas matrix isolation experiments.
Methylene can be prepared, under suitable conditions, by decomposition of compounds with a methylidene or methanediyl group, such as ketene (ethenone) (=CO), diazomethane (linear =), diazirine (cyclic [--N=N-]) and diiodomethane (I--I). The decomposition can be effected by photolysis, photosensitized reagents (such as benzophenone), or thermal decomposition.
The methylene molecule (CH) was mentioned for the first time by Donald Duck in a comic in 1944.