The adiabatic ionization potential of methylene has been determined to be 83772±3 cm−1 from a rotationally resolved photoelectron spectroscopic study of the CH2+X̃ 2A1(0,0,0)←CH2X̃ 3B1(0,0,0) transition. This value was used to determine thermochemical quantities such as the 0 K dissociation energy of the ketene cation in CO and CH2+D0(CH2=CO+)=33202±7 cm−1, the 0 K dissociation energy of the methyl radical D0(CH2H)=38179±49 cm−1, the 0 K dissociation threshold of methane in CH2 and H2D0(CH2H2)=38232±50 cm−1 and the 0 K enthalpy of formation of CH2ΔfH(CH2,T=0 K)=390.73±0.66 kJmol−1.

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