Neutral clusters analog

With free jet expansion techniques, we have produced clusters of aqueous nitric acid (3 ), hydrochloric acid, sulfuric acid (4, pure acetic acid ( 5), and sulfur dioxide (6). For analogy to buffering, the formation of clusters containing ammonia have also been examined. These have included ammonia with aqueous nitric acid (7 ), hydrogen sulfide (7J), and sulfur dioxide (8). The basic experiment involves expansion of vapor through a nozzle, collima-tion of the jet with a skimmer to form a well-directed molecular beam, and detection of clusters via electron impact ionization and quadrupole mass spectrometry. Some variations include the introduction of a reactive gas into vacuum near the expansion as described elsewhere (4, 8) and the implementation of an electrostatic quadrupolar field to examine the polarity of the neutral clusters. The electric deflection technique is described by Klemperer and coworkers (9). 

The iron-selenium cubane-type cluster [Fe4Se4(NO)4] has been shown (52) to adopt a molecular structure of almost exact Td symmetry, whereas in the corresponding anion [Fe4Se4(N0)4] the symmetry is lowered to D2a, just as for the sulfur analogs (37). Upon one-electron reduction the size of the Fe4 cage increases in the neutral molecule the Fe-Fe and Fe-Se distances are 2.703 and 2.342 A, but in the anion the... 

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