Experimental studies of the dissociative recombination processes for the dimethyl ether ions CD3OCD2+ and (CD3)2OD

Aims: Determination of branching fractions, cross sections and thermal rate coefficients for the dissociative recombination of CD 3 OCD 2 + (0-0.3 eV) and (CD 3 ) 2 OD+ (0-0.2 eV) at the low relative kinetic energies encountered in the interstellar medium. Methods: The measurements were carried out using merged electron and ion beams at the CRYRING storage ring, Stockholm, Sweden. Results: For (CD 3 ) 2 OD+ we have experimentally determined the branching fraction for ejection of a single hydrogen atom in the DR process to be maximally 7% whereas 49% of the reactions involve the break up of the COC chain into two heavy fragments and 44% ruptures both C-O bonds. The DR of CD 3 OCD 2 + is dominated by fragmentation of the COC chain into two heavy fragments. The measured thermal rate constants and cross sections are k(T) =1.7 ± 0.5 × 10 − 6 (T/300) − 0 . 77 ±0.01 cm3s−1, σ= 1.2 ± 0.4 × 10 − 15 (Ecm[eV]) − 1 . 27 ± 0 . 01 cm 2 and k(T) = 1.7 ± 0.6 × 10 − 6 (T/300) − 0 . 70 ± 0 . 02 cm 3 s − 1 ,σ= 1.7 ± 0.6 × 10 − 15 (Ecm[eV]) − 1 . 20 ± 0 . 02 cm 2 for CD 3 OCD 2 + and (CD 3 ) 2 OD + , respectively.