摘要：

First direct experimental evidence for clathrate structures of (H2O) n H+ (n=20,21) is reported based on a technique allowing the number of nonhydrogen‐bonded surface hydrogens to be counted. Neutral clusters (H2O) n ((CH3)3N) m , prepared in a pulsed nozzle supersonic expansion, are ionized by multiphoton ionization and investigated with a reflectron time‐of‐flight mass spectrometry technique. The magic numbers (n,m) in the ion intensity distributions of (H2O) n ((CH3)3N) m H+ studied under various experimental conditions are well correlated to the stable hydrogen‐bonding structures. For the mixed cluster ion (H2O)2 0((CH3)3N) m H+, the intensity distribution displays an abrupt intensity drop after the magic number at (20,11), while for (H2O)2 1((CH3)3N) m H+ the magic number appears at (21,10). The findings provide experimental evidence for a stable clathrate structure of (H2O)2 0H+, with the proton residing on the surface, while for (H2O)2 1H+, the H3O+ ion is encaged inside the clathrate structure of (H2O)2 0; the latter structure provides a total of 10 hydrogen‐bonding sites for (CH3)3N.

展开