화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.125, No.7, 1402-1412, 2021
Laser-Induced Fluorescence Spectroscopy of Large Secondary Alkoxy Radicals: Part II. Rotational and Fine Structure
Selected vibronic bands of the (B) over tilde <- (X) over tilde laser-induced fluorescence (LIF) spectra of jet-cooled 2-pentoxy and 2-hexoxy, including the origin and CO-stretch bands, have been measured with rotational resolution and analyzed using (1) an effective Hamiltonian that comprises a rotational part and a spin-rotation (SR) part (the "isolated-states model") and (2) a recently developed Hamiltonian in which the nearly degenerate (A) over tilde and (X) over tilde states are treated together (the "coupled-states model") (see Liu, J., J. Chem. Phys. 2018, 148, 124112). The observed rotational and fine structures of the strongest vibronic bands have first been simulated using a genetic algorithm with the isolated-states model. The parameters for the simulation include rotational constants for both the (X) over tilde and (B) over tilde states, which can be calculated from the electronic structure theory, as well as the electronic SR constants of the (X) over tilde state and the transition dipole moments (TDMs), both of which are predicted based on their transferability in an "orbital-fixed coordinate system" using iso-propoxy as the reference molecule. Quantum chemistry calculations suggest that the lowest two electronic ((X) over tilde and (A) over tilde) states of secondary alkoxy radicals have small energy separations on the order of 100 cm(-1) (see Part I of this series: J. Phys. Chem. A 2021, DOI: 10.1021/sics.ipca.0c10662). The electron configurations of these two nearly degenerate states have been determined by comparing the experimentally determined rotational constants and the TDMs to the ones predicted for the X and A states. The experimental LIF spectra were also simulated with the coupled-states model, in which the effective spin-orbit (SO) constants (a zeta(e)d) and the SO-free separation between the A and the (X) over tilde states (Delta E-0) have been determined. Molecular constants derived from fitting the rotational and fine structures of the experimental LIF spectra enabled unambiguous assignment of the observed vibronic bands to specific conformers of 2-pentoxy and 2-hexoxy as reported in Part I.