H−formation from collisional destruction of fastH3+ions in noble gases

We have studied the production of ${\mathrm{H}}^{\mathrm{-}}$ by fast ${\mathrm{H}}_3^{+}$ ions (4≤v≤7 a.u.) colliding with He, Ne, Ar, and Xe atoms. The negative-ion yields were measured as a function of target pressure and from them were extracted the ${\mathrm{H}}^{\mathrm{-}}$ production cross sections, the maximum yields, and the pressure values associated with these maxima. We observed that the maximum yield is about the same for all gases and velocities in the range under consideration. This fact reveals an almost identical scaling for the ${\mathrm{H}}^{\mathrm{-}}$ production, the ${\mathrm{H}}_3^{+}$ destruction, and the ${\mathrm{H}}^{\mathrm{-}}$ destruction cross sections. The ratio of the ${\mathrm{H}}^{\mathrm{-}}$ production and the ${\mathrm{H}}_3^{+}$ destruction cross sections was also verified to assume essentially the same value for all measurements. The cross sections were well fitted by a semiempirical version of the free collision model.