Experimental study of recombination of H-3(+) ions with electrons relevantfor interstellar and planetary plasmas

The H-3(+) is a key ion in the interstellar chemistry. The rate of recombin ation of H-3(+) with electrons, alpha, plays a pivotal role in the level of ionization of interstellar plasmas. Over the past 50 years a number of stu dies of this recombination have been carried out, yet they did not lead to an unambiguous value of alpha. We report observation of the rate of de-ioni zation of H-3(+) as low as alpha (eff) similar to 3 x 10(-9) cm(3) s(-1) at hydrogen density decreasing down to 5 x 10(10) cm(-3). This implies that t he dissociative recombination of H-3(+) under interstellar conditions is ve ry slow with alpha (DR) much less than 10(-8) cm(3) s(-1). This value is in agreement with theoretical predictions and astronomical observations, and provides an explanation of the 'enigma of H-3(+)'.