Table 1. Center frequencies of the lines in the P(4) manifold of the ν ₃ band of ¹²CH₄ measured in this work along with a comparison with the accurate measurements reported in Ref. 32 by Doppler-free saturated absorption spectroscopy and in Ref. 22 by Doppler-limited dual-comb spectroscopy.

Assignment	Frequency (MHz)
	This work	Ref. 32	This work−Ref. 32	Ref. 22	This work−Ref. 22
P(4) F2(1)	89 297 694.9 (12)	89 297 695.2635 (20)	−0.4	89 297 695.06 (30)	−0.2
P(4) E(1)	89 303 617.9 (13)	89 303 620.0492 (20)	−2.1	89 303 619.87 (30)	−2.0
P(4) F1(1)	89 305 771.5 (11)	89 305 771.6093 (20)	−0.1	89 305 771.40 (30)	0.1
P(4) A1(1)	89 308 513.3 (11)	89 308 512.2568 (20)	1.0	89 308 512.19 (30)	1.1