Modeling the CH Stretch/Torsion/Rotation Couplings in Methyl Peroxy (CH₃OO)

Abstract

The manifestations of CH stretch/torsion/rotation coupling in the region of the CH stretch fundamentals are explored in the CHOO radical. Following our earlier study of the fundamental in the totally symmetric CH stretch (the ν fundamental), this work focuses on the other two CH stretch fundamentals, ν and ν, which would be degenerate in the absence of a barrier in the potential along the methyl torsion coordinate. The simplest model, which assumes a decoupling of the CH stretch vibrations from the torsion, fails to reproduce several important features of the spectrum. Specifically, the absence of a strong peak around the origin of the ν fundamental and broadening of the strong peak near the origin in the observed spectrum of the ν fundamental are not captured by this model. The origins of these features are explored through two more sophisticated treatments of the torsion/CH stretch couplings. In the first, a four-dimensional potential based on the three CH stretches and the torsion is developed and shown to reproduce both of these features. On the basis of the results of these calculations, the calculated parameters are adjusted to simulate the recorded spectrum. To further explore the torsion/CH stretch couplings in CHOO, a 9-state model Hamiltonian is developed and discussed. The implications of various types of couplings on the observed energy level patterns are also discussed.

Anharmonic Rovibrational Partition Functions at High Temperatures: Tests of Reduced-Dimensional Models for Systems with up to Three Fluxional Modes

“…A variety of theoretical methods have been advanced for characterizing rovibrational anharmonicity, including diffusion Monte Carlo, , variational approaches, − path integrals, − direct product diagonalization, − empirical methods, , perturbation theories, − specialized methods for torsions, − and other separable approaches. − Many of these methods are designed for spectroscopic applications and are most reliably applied to predict high-accuracy zero point energies and fundamental transition energies. There has been relatively less work done to characterize anharmonicity at high temperatures and energies.…”

Photodissociation dynamics of the simplest alkyl peroxy radicals, CH3OO and C2H5OO, at 248 nm

“…10,11 Step-scan Fourier transform spectroscopy has been used to obtain temporally resolved IR spectra for CH 3 OO, identifying major absorption bands and characterizing the torsional splitting of the ν 1 , ν 2, and ν 9 modes. [12][13][14] Blanksby et al 15 have reported the photoelectron (PE) spectra of the CH 3 OO and C 2 H 5 OO anions, finding the electron affinities of the corresponding radicals to be 1.161 ± 0.005 eV and 1.186 ± 0.004 eV, respectively. Theà ←X electronic transitions of CH 3 OO and C 2 H 5 OO in the near-IR absorption region have been characterized by Miller and co-workers [16][17][18] using cavity ringdown spectroscopy.…”

Simultaneous determination of transient free radicals and reaction kinetics by high-resolution time-resolved dual-comb spectroscopy

“…Thus, the proposed method is promising for in situ time-resolved measurements and remote sensing to explore the issues in atmospheric chemistry and other applied sciences. Future studies can perform quantitative spectral analysis with rotationally resolved spectra of key radicals, such as organic peroxy radicals (RO 2 ) with torsion-CH stretch coupled infrared spectral features 42 . Unstable molecules, such as the simplest Criegee intermediate 2 , which has relatively weak C-H vibrational bands, can also be observed with our time-resolved dual-comb spectrometer coupled with a cavity-enhanced cell.…”