THE NATURE OF AMMONIUM AND METHYLAMMONIUM HALIDES IN THE VAPOR-PHASE - HYDROGEN-BONDING VERSUS PROTON-TRANSFER

The familiar white smoke, so redolent of school chemistry, is the ultimate product when ammonia and hydrogen chloride gases mix but what is the nature of the heterodimer first formed? Is it the simple hydrogen-bonded species H3N...HCl or is the proton transferred to give the ion pair H3NH+...Cl-? How is the extent of proton transfer affected by progressive methylation of NH3. by replacement of Cl with Br and then I, and by substitution of N by P? Recent advances in the rotational spectroscopy of supersonically expanded jets have led to answers to these fundamental questions.