The spectroscopic characterization of the methoxy radical. I. Rotationally resolved Ã A21–X̃ E2 electronic spectra of CH3O

Abstract

New experimental data have been obtained for the methoxy radical by observing at high-resolution laser-induced fluorescence (LIF) and stimulated emission pumping (SEP) transitions between the X (2)E and lowest excited A (2)A(1) state. The SEP transitions were from the A state (pumped from the X (2)E(3/2) spin-orbit component) to the X (2)E(1/2) spin-orbit component. These data for the first time directly connect with high precision the spin-orbit components of the X (2)E ground state of CH(3)O. Surprisingly these new SEP observations are inconsistent with predictions of the X state structure based on long-standing analyses primarily based on the microwave spectra of ground state CH(3)O. It is found that all the experimental data can be understood consistently when the previously accepted value of the spin-orbit coupling constant is adjusted and the reflection parity assignments in the X state are reversed. The latter action changes the sign of a number of reflection-parity-dependent parameters in the X state. The ramifications of the changes and the physical interpretation of the resulting parameters are discussed in some detail.

Rotationally resolved ${\tilde{B}} \leftarrow {\tilde{X}}$B̃←X̃ electronic spectra of the isopropoxy radical: A comparative study

“…8 and references therein.) Recently, 9,10 we reported A 2 A 1 −X 2 E 3/2 LIF andà 2 A 1 −X 2 E 1/2 stimulated emissionpumping (SEP) spectra of CH 3 O and its fully deuterated isotopologue (CD 3 O) with rotational and fine-structure resolution and frequency accuracy of ∼50 MHz. ( 2 E 1/2 and 2 E 3/2 are the upper and lower spin-orbit components of the ground electronic state, respectively.)…”

Photoelectron spectroscopic study of the E⊗e Jahn–Teller effect in the presence of a tunable spin–orbit interaction. I. Photoionization dynamics of methyl iodide and rotational fine structure of CH3I+ and CD3I+

“…26 Despite these studies, the rovibronic structures of the methyl-halide cations remain less well characterized and understood than is the case for the corresponding isoelectronic neutral molecules CH 3 O and CH 3 S, for which high-resolution spectra have been obtained and analyzed. 3,[27][28][29][30] The methoxy radical, in particular, has served as a prototypical molecule to study the Jahn-Teller effect and spin-orbit coupling, and represents one of the best understood molecular systems subject to the E ⊗ e Jahn-Teller effect (see Refs. 3, 27, 29, and 30 and references therein).…”

The spectroscopic characterization of the methoxy radical. III. Rotationally resolved $\skew3\tilde{A}^2A_1\text{–}\skew3\tilde{X}^2E$Ã2A1–X̃2E electronic and $\skew3\tilde{X}^2E$X̃2E submillimeter wave spectra of partially deuterated CH2DO and CHD2O radicals

“…One possible approach to the dissociation dynamics in methoxy is to produce a unique C-H stretch motion by asymmetric deuteration to form CHD 2 O. The study of asymmetrically substituted methoxy radicals is also important from spectroscopic and quantum chemical points of view, since it is small enough to completely resolve the rotational and spin structure of both microwave and electronic spectra, and a rather complete analysis 10,20,21 has been reported for CH 3 O, 13 CH 3 O, and CD 3 O. Methoxy radicals with one or two deuterons have a nuclear symmetry corresponding to the MS group isomorphous with the C s rather than the C 3v point group, and the Jahn-Teller effect transforms into a pseudo Jahn-Teller effect. Efforts have been made in only a few cases, e.g., cyclopentadienyl 22 and methane cation 23,24 to analyze the rotational spectra of an asymmetric isotopologue of a Jahn-Teller molecule.…”