Deduction of the geometry of the methyl anion from a potential function calculation on the corresponding photoelectron spectrum

The photoelectron spectrum of methyl anion was simulated by invoking a potential function of V(q) = q 2/2 + σR q 4 for methyl radical with σR = 0·085 and a double-minimum potential V(q) = q 2/2 + σA q 4 + κ exp (-ζq 4) with σA = 0·005, κ = 16·629 and ζ = 0·050 by considering the out-of-plane vibration (ν2) alone. The agreement between the theoretical and the experimental spectra is excellent. From the intensity calculation, the bond angle and the inversion barrier of the anion are found to be respectively 108· ± 1·4° and 705 ± 40 cm-1 in comparison with values of 110° and 620 to 680 cm-1 from an ab initio calculation [11]. From another Franck-Condon factor calculation, the bond length of CH- 3 is estimated to be close to that of CH3 probably within 0·025 A.