First investigation at elevated pressures to confirm the exact nature of the gated electron-transfer systems: Volume profiles of the gated reduction reaction and nongated reverse oxidation reaction involving a [[Cu[(dmp).sub.2](solvent)].sup.2+]/[[Cu[(dmp).sub.2]].sup.2+] couple (dmp=2,9,dimethyl-1,10-phenanthroline)

Gated redox reactions involving the [[Cu[(dmp).sub.2](solvent)].sup.2+]/[[Cu[(dmp).sub.2]].sup.2+] couple (dmp=2,9,dimethyl-1,10-phenanthroline) in acetonitrile were investigated at elevated pressures. The results led to conclusion that the reverse cross-reaction of the gated reduction of the [[Cu[(dmp).sub.2](solvent)].sup.2+]/[[Cu[(dmp).sub.2]].sup.2+] couple proceeds through the product excited state while the direct self-exchange reaction proceeds through an ordinary process.