Amplifiers, unimolecular

Fig. 31 Proposed unimolecular amplifier DiD2A, in a circuit analogous to a grounded-emitter junction transistor, grounded-source FET, or grounded-cathode triode circuit. The arrows show the direction of preferred electron flow. The two Au and one A1 electrode tips must be about 3 nm apart...

At present making the first unimolecular amplifier is mainly hampered by the experimental difficulty in placing three electrodes 3 nm apart from each other. As discussed above, MCBJs and EMBJs have yielded reproducible 1-3 nm gaps between two electrodes the third gate electrode can be an STM tip or a CP-AFM tip or an oxide-covered A1 electrode. 

Long et al. (1957), amplifying a suggestion of Taft and co-workers (1955), have proposed the use of AS as a criterion of the mechanism of hydrolysis reactions. These reactions are usually classified as unimolecular (A-l, SN-1) or bimolecular (A-2, SN-2). In the former case a water molecule does not participate in the rate-determining step, while a water molecule is usually considered to be bound in the activated... 

It has been found possible to extend and amplify QMOT procedures so that they apply to chemical reactions. One of the most striking examples of this was application to unimolecular cyclization of an open conjugated molecule (e.g., cw-1,3-butadiene, closing to cyclobutene). This type of reaction is called an electrocyclic reaction. The details of the electrocyclic closure of cw-1,3-butadiene are indicated in Fig. 14-17. 

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