The H3+ molecular ion plays a fundamental role in interstellar chemistry, as it initiates a network of chemical reactions that produce many molecules. In dense interstellar clouds, the H3+ abundance is understood using a simple chemical model, from which observations of H3+ yield valuable estimates of cloud path length, density and temperature. But observations of diffuse clouds have suggested that H3+ is considerably more abundant than expected from the chemical models. Models of diffuse clouds have, however, been hampered by the uncertain values of three key parameters: the rate of H3+ destruction by electrons (e-), the electron fraction, and the cosmic-ray ionization rate. Here we report a direct experimental measurement of the H3+ destruction rate under nearly interstellar conditions. We also report the observation of H3+ in a diffuse cloud (towards Persei) where the electron fraction is already known. From these, we find that the cosmic-ray ionization rate along this line of sight is 40 times faster than previously assumed. If such a high cosmic-ray flux is ubiquitous in diffuse clouds, the discrepancy between chemical models and the previous observations of H3+ can be resolved.

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The branching ratios of the different reaction pathways and the overall rate coefficients of the dissociative recombination reactions of CH 3 OH 2 + and CD 3 OD 2 + have been measured at the CRYRING storage ring located in Stockholm, Sweden. Analysis of the data yielded the result that formation of methanol or deuterated methanol accounted for only 3 and 6% of the total rate in CH 3 OH 2 + and CD 3 OD 2 + , respectively. Dissociative recombination of both isotopomeres mainly involves fragmentation of the C-O bond, the major process being the three-body break-up forming CH 3 , OH and H (CD 3 , OD and D). The overall cross sections are best fitted by s = 1.2 AE 0.1 Â 10 À15 E À1.15AE0.02 cm 2 and s = 9.6 AE 0.9 Â 10 À16 E À1.20AE0.02 cm 2 for CH 3 OH 2 + and CD 3 OD 2 + , respectively. From these values thermal reaction rate coefficients of k(T) = 8.9 AE 0.9 Â 10 À7 (T/300) À0.59AE0.02 cm 3 s À1 (CH 3 OH 2 + ) and k(T) = 9.1 AE 0.9 Â 10 À7 (T/300) À0.63AE0.02 cm 3 s À1 (CD 3 OD 2 + ) can be calculated. A non-negligible formation of interstellar methanol by the previously proposed mechanism via radiative association of CH 3 + and H 2 O and subsequent dissociative recombination of the resulting CH 3 OH 2 + ion to yield methanol and hydrogen atoms is therefore very unlikely.

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