Vibrational mode selective, radiationless transitions have been sought in the [Formula: see text] states of [Formula: see text] and [Formula: see text] by determining the radiative kr(ν′) and nonradiative knr(ν′) rates of electronic relaxation of energy selected vibronic levels of these cations. The relaxation rates were derived from measurements of ion fluorescence quantum yields and lifetimes using a photoelectron-fluorescence photon delayed coincidence apparatus, described in the text, in which the ions are formed by direct photoionization. Mode selective behavior is confirmed for the ν1 and ν2 modes of the [Formula: see text] state of [Formula: see text], previously studied by a threshold photoelectron-fluorescence photon coincidence method in which photoion formation involved auto-ionization as well as direct photoionization. In the case of the ν3 and ν4 modes of [Formula: see text], knr(ν′) was found to depend only on the excess energy Eν′ in the [Formula: see text] state and not on the particular mode optically excited. The absence of mode selectivity in this cation could be due to very rapid vibrational redistribution, but more probably results from similar-valued nonradiative coupling matrix elements of vibronic levels involving ν3 and (or) ν4 modes for a given value of Eν′. This is shown to be consistent with the known spectroscopic properties of [Formula: see text].