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Diatomic UO has more than 48 bound states within 10000 cm^-1 of the ground state. This electronic state congestion has been attributed to interleaved states from the electronic configurations U²⁺($5f^37s$)O^2- and U²⁺($5f^27s^2$)O^2-, respectively. Ligand field theory predicts that each electronic configuration will exhibit states with distinguishable, characteristic vibrational and rotational constants. However, vibronic state mixing modifies the observed vibration–rotation constants, leading to uncertainty in the configurational assignments. The permanent electric dipole moment ($$μ_e$$) of an electronic state should also manifest a value that is characteristic of the parent electronic configuration. $$μ_e$$ and other electrostatic and magnetostatic properties should be lessmore » influenced by the vibronic state mixing, providing more robust indicators for configurational assignments. In the present study, we have measured the $$μ_e$$ values for four electronic states of UO. Here, the results clearly demonstrate that the ground state (X(1)4) and the first electronically excited state ((2)4) are derived from the U²⁺($5f^37s$)O^2– and U²⁺($5f^27s^2$)O^2– configurations, respectively.« less

We used transient diode laser absorption spectroscopy to measure three strong vibronic bands in the near infrared spectrum of the C₂H, ethynyl, radical not previously observed in the gas phase. The radical was produced by ultraviolet excimer laser photolysis of either acetylene or (1,1,1)-trifluoropropyne in a slowly flowing sample of the precursor diluted in inert gas, and the spectral resolution was Doppler-limited. The character of the upper states was determined from the rotational and fine structure in the observed spectra and assigned by measurement of ground state rotational combination differences. The upper states include a ²Σ⁺ state at 6696 cm^-1,more » a second ²Σ⁺ state at 7088 cm^-1, and a ²Π state at 7110 cm^-1. By comparison with published calculations [R. Tarroni and S. Carter, J. Chem. Phys 119, 12878 (2003); Mol. Phys. 102, 2167 (2004)], the vibronic character of these levels was also assigned. Moreover, the observed states contain both X ²Σ⁺ and A ²Π electronic characters. Several local rotational level perturbations were observed in the excited states. Kinetic measurements of the time-evolution of the ground state populations following collisional relaxation and reactive loss of the radicals formed in a hot, non-thermal, population distribution were made using some of the strong rotational lines observed. Finally, the case of C₂H may be a good place to investigate the behavior at intermediate pressures of inert colliders, where the competition between relaxation and reaction can be tuned and observed to compare with master equation models, rather than deliberately suppressed to measure thermal rate constants.« less