The b̃¹B₁←ã ¹A₁ spectrum of CH₂ radical has been recorded with Doppler‐limited resolution in the 15 600–18 650 cm⁻¹ wavelength region by laser flash‐kinetic absorption spectroscopy. Singlet methylene is produced by photolysis of ketene at 308 nm. Assignments for 477 transitions originating from ¹A₁(0,0,0) and (0,1,0) levels with J≤8 and K_a≤5 are reported from some 10 000 lines observed. Term values are given for these ¹A₁ levels and ¹B₁(0,v₂,0) levels with 13≤v₂≤17. Magnetic‐rotation signals were observed for 60% of the 424 lines studied. This anomalous Zeeman effect is explained by singlet–triplet mixing in both ã and b̃ states. Extensive singlet–triplet mixing occurs for ¹B₁ levels with K_a≠0; this mixing is allowed in second order by Renner–Teller coupling of b̃ ¹B₁ with ã ¹A₁ and by spin‐orbit coupling via ã ¹A₁ to X̃ ³B₁. The consequent shifts prevent determination of accurate rovibrational structural parameters for the ¹B₁ state.

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