Journal of Chemical Physics, Vol.113, No.20, 8945-8952, 2000
Ultraviolet laser spectroscopy of jet-cooled CaNC and SrNC free radicals: Observation of bent excited electronic states
New electronic transitions of the CaNC and SrNC free radicals have been identified in the near ultraviolet. For CaNC one new system, labeled the (D) over tilde-(X) over tilde transition, was observed in the 31 500-33 400 cm(-1) region. Two new transitions were found for SrNC, the (D) over tilde-(X) over tilde and (E) over tilde-(x) over tilde systems spanning 29 100-31 000 and 32 750-34 000 cm(-1), respectively. Jet-cooled laser excitation spectra yield complex vibrational structure, much of which is attributed to excitation of the bending vibration. This has been used to infer that the molecule adopts a nonlinear equilibrium geometry in the upper electronic state in all three band systems, in contrast to the linear ground electronic state. This structural change is accounted for by the increased diffuseness of the unpaired electron in the excited states, which favors deviation from linearity. All three new excited states are assigned (2)A' symmetry and correlate with (2)Sigma (+) states in the linear molecule limit. Tentative estimates for the barriers to linearity in the (D) over tilde (2)A' states of CaNC and SrNC have been determined as similar to 700 and similar to 1050 cm(-1), respectively.