Observation of the electromagnetic Dalitz transition hc ? e plus e-?c

Using (27.12 +/- 0.14) x 10(8) psi(3686) decays and data samples of e(+)e(-) collisions with root s from 4.130 to 4.780 GeV collected with the BESIII detector, we report the first observation of the electromagnetic Dalitz transition h(c) -> e(+)e(-)eta(c) with a statistical significance of 5.4 sigma. We measure the ratio of the branching fractions B(h(c) -> e(+)e(-)eta(c))/B(h(c) -> gamma eta(c)) separately for the h(c) samples produced via psi(3686) -> pi(0)h(c) and e(+)e(-) -> pi(+)pi(-)h(c). The average ratio is determined to be (0.59 +/- 0.10(stat) +/- 0.04(syst))%, where the uncertainty includes both statistical and systematic components.