Abstract
General techniques of the QCD multipole expansion are developed and applied to the study of soft-gluon effects in quarkonium decays. In contrast to short-distance corrections, nonperturbative QCD corrections turn out to reduce the ratio GAMMA(eta/sub c/..-->..2..gamma..)/GAMMA (J/psi..-->..e/sup +/e/sup -/); the ratio GAMMA(eta/sub c/..-->..2..gamma..)/GAMMA(eta/sub c/..-->..2g) thereby remains unaffected. An application to the QCD sum rules is also presented; multipole-expansion techniques provide a systematic and powerful means of calculating nonperturbative terms in the sum-rule approach.
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