Lanthanide metal atoms, produced by laser ablation, were condensed with CH3F in excess Ar at 8 K New infrared absorption bands are assigned to the first insertion CH(3)LnF and oxidative addition methylene lanthanide hydride fluoride CH(2)LnHF products on the basis of C-13 and deuterium substitution and density functional theory calculations of the vibrational frequencies. It is also possible to observe the cationic species CH(3)LnF(+) for some Ln. For Ln = Eu and Yb, only CH(3)LnF is observed. CH(3)LnF in the Ln formal +2 state is predicted to be more stable than CH(2)LnHF with the Ln in the formal +3 oxidation state. CH3-LnF forms a single bond between Ln and C and is a substituted methane. Similar to CH2-LnF(2), CH2-LnHF does not form a pi-bond between Ln and C and is best described as a LnHF-substituted CH3 radical, with an unpaired p electron on C weakly interacting with the unpaired f electrons on the Ln. The calculated potential energy surface for the CH3F + La -> CH3-LaF/CH2-LaHF shows a number of intermediates and transition states on multiple paths. The reaction mechanism involves the potential formation of LaF and LaHF intermediates.