The C̃–X̃ electronic spectrum of the SrNC free radical: a jet-cooled investigation

The quasi-continuous band system of the SrNC free radical first observed many years ago by Pasternack and Dagdigian, and attributed to the C̃–X̃ electronic transition, has been subjected to a jet-cooled laser-induced fluorescence study. This new work reveals abundant vibrational structure that was largely hidden in the earlier study. The spectrum is not amenable to a simple vibrational analysis, presumably because of extensive perturbations. However, the fact that the structure spans more than 3500 cm−1 reveals that SrNC undergoes a major geometry change on electronic excitation. Since it is known to be linear in its ground electronic state (2Σ+), the activity of the bending vibration in the spectrum suggests that SrNC adopts a nonlinear equilibrium geometry on excitation.