Meson decay constants from isospin mass splittings in the quark model.

Decay constants of [ital D] and [ital B] mesons are estimated within the framework of a heavy-quark approach using measured isospin mass splittings in the [ital D], [ital D][sup *], [ital B], and [ital B][sup *] states to isolate the electromagnetic hyperfine interaction between quarks. A relation following from the use of splittings in kaons is also considered.