Observation of several new electronic transitions of the SrOH free radical

We report four new electronic transitions of the SrOH free radical, the (C) over tilde (2)Pi-(X) over tilde (2)Sigma(+), (D) over tilde (2)Sigma(+) - (X) over tilde (2)Sigma(+), (E) over tilde (2)Sigma(+) - (X) over tilde (2)Sigma(+) and (F) over tilde (2)Pi - (X) over tilde (2)Sigma(+) transitions. SrOH was prepared in a supersonic jet by laser ablation and spectra were recorded using laser-induced fluorescence. The (C) over tilde (2)Pi - (X) over tilde (2)Sigma(+) excitation spectrum shows complex vibronic structure which is attributed, at least in part, to Renner-Teller activity in the excited electronic state. This is supported by dispersed fluorescence spectra which show substantial bending mode activity in the emission from several different excited vibronic levels. It is suggested that the prominence of nominally forbidden vibrational features arises from a large change in permanent electric dipole moment between the (X) over tilde and (C) over tilde states. In turn, this suggests that the (C) over tilde (2)Pi state of SrOH is the analogue of the "reverse-polarized'' (2)Pi states known for the alkaline-earth monohalides, i.e., the highest occupied pi orbital points towards the O atom. The (D) over tilde (2)Sigma(+) - (X) over tilde (2)Sigma(+), (E) over tilde 2 Sigma+ - (X) over tilde (2)Sigma(+), and (F) over tilde (2)Pi - (X) over tilde (2)Sigma(+) spectra are much simpler than the (C) over tilde - (X) over tilde system, being dominated by regular structure in the Sr-O stretching vibration. (C) 1999 American Institute of Physics. [S0021-9606(99)01023-5].