SIMBAD references

Specific chemical signatures of the intermittent dissipation of turbulence were sought in diffuse molecular clouds. We observed HCO⁺(1-0) lines and the two lowest rotational transitions of ¹²CO and ¹³CO with an exceptional signal-to-noise ratio in the translucent environment of low-mass dense cores, where turbulence dissipation is expected to take place. Some of the observed positions belong to a new kind of small-scale structure identified in CO(1-0) maps of these environments as the locus of non-Gaussian velocity shears in the statistics of their turbulent velocity field, i.e. singular regions generated by the intermittent dissipation of turbulence. We report the detection of broad HCO⁺(1-0) lines (10mK<T_A^*<0.5K). We achieve the interpretation of ten HCO⁺ velocity components by conducting it in conjunction with that of the associated optically thin ¹³CO emission. The derived HCO⁺ column densities span a broad range, 10¹¹<N(HCO⁺)/Δv<4x10¹²/cm²/km/s, and the inferred HCO⁺ abundances, 2x10^–10<X(HCO⁺)<10^–8, are more than one order of magnitude above those produced by steady-state chemistry in gas that is weakly shielded from UV photons, even at large densities. We compare our results with predictions of non-equilibrium chemistry, swiftly triggered in bursts of turbulence dissipation and followed by a slow thermal and chemical relaxation phase, assumed to be isobaric. The set of values derived from observations, i.e. large HCO⁺ abundances, temperatures in the range of 100-200K, and densities in the range 100-10³cm^–3, unambiguously belongs to the relaxation phase. In contrast, the kinematic properties of the gas suggest that the observed HCO⁺ line emission results from a space-time average in the beam of the whole cycle followed by the gas and that the chemical enrichment is made at the expense of the non-thermal energy. Last, we show that the ``warm chemistry'' signature (i.e. large abundances of HCO⁺, CH⁺, H₂O, and OH) acquired by the gas within a few hundred years, which is the duration of the impulsive chemical enrichment, is kept over more than a thousand years. During the relaxation phase, the H₂O/OH abundance ratio stays close to the value measured in diffuse gas by the SWAS satellite, while the OH/HCO⁺ ratio increases by more than one order of magnitude.