High-resolution cavity ringdown spectroscopy of the jet-cooled ethyl peroxy radical C2H5O2

An effective Hamiltonian without symmetry restriction has been developed to model the rotational and fine structure of two nearly degenerate electronic states of an open-shell molecule. In addition to the rotational Hamiltonian for an asymmetric top, this spectroscopic model includes the energy separation between the two states due to difference potential and zero-point energy difference, as well as the spin-orbit (SO), Coriolis, and electron spin-molecular rotation (SR) interactions. Hamiltonian matrices are computed using orbitally and fully symmetrized case (a) and case (b) basis sets. Intensity formulae and selection rules for rotational transitions between a pair of nearly degenerate states and a nondegenerate state have also been derived using all four basis sets. It is demonstrated using real examples of free radicals that the fine structure of a single electronic state can be simulated with either a SR tensor or a combination of SO and Coriolis constants. The related molecular constants can be determined precisely only when all interacting levels are simulated simultaneously. The present study suggests that analysis of rotational and fine structure can provide quantitative insights into vibronic interactions and related effects.

Section: Sr Constantsmentioning

confidence: 99%

Rotational and fine structure of open-shell molecules in nearly degenerate electronic states

Liu

2018

“…[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. TheÃ ←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. For both radicals, ground state andÃ state rovibronic structures were observed and identified.…”

Section: Introductionmentioning

confidence: 99%

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

Sullivan

Nichols

Neumark

2018

The photodissociation dynamics of the simplest alkyl peroxy radicals, methyl peroxy (CHOO) and ethyl peroxy (CHOO), are investigated using fast beam photofragment translational spectroscopy. A fast beam of CHOO or CHOO anions is photodetached to generate neutral radicals that are subsequently dissociated using 248 nm photons. The coincident detection of the photofragment positions and arrival times allows for the determination of mass, translational energy, and angular distributions for both two-body and three-body dissociation events. CHOO exhibits repulsive O loss resulting in the formation of O(D) + CHO with high translational energy release. Minor two-body channels leading to OH + CHO and CHO + O(P) formation are also detected. In addition, small amounts of H + O(P) + CHO are observed and attributed to O loss followed by CHO dissociation. CHOO exhibits more complex dissociation dynamics, in which O loss and OH loss occur in roughly equivalent amounts with O(D) formed as the dominant O atom electronic state via dissociation on a repulsive surface. Minor two-body channels leading to the formation of O + CH and HO + CH are also observed and attributed to a ground state dissociation pathway following internal conversion. Additionally, CHOO dissociation yields a three-body product channel, CH + O(P) + CHO, for which the proposed mechanism is repulsive O loss followed by the dissociation of CHO over a barrier. These results are compared to a recent study of tert-butyl peroxy (t-BuOO) in which 248 nm excitation results in three-body dissociation and ground state two-body dissociation but no O(D) production.

“…[5][6][7][8] Details about the present experimental work not described in the previous papers will be described in this section.…”

Section: Methodsmentioning

confidence: 99%

“…However, the excitedÃ electronic state is bound and produces spectra that distinguish among different chemical species and their isomers and conformers because of the sharp vibrational and rotational structure. 4 Jet cooled high-resolution cavity ringdown spectroscopy (CRDS) studies on peroxy radicals [5][6][7] are useful for diagnostic purposes, experimentally characterizing the molecule, and benchmarking quantum chemical calculations. 8 The β-hydroxyethylperoxy (2-hydroxyethylperoxy) radical in the atmosphere arises from the reaction of ethene (CH 2 CH 2 ) and hydroxy radical (OH), followed by reaction with oxygen (O 2 ).…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic studies of the $\tilde{A}$Ã–$\tilde{X}$X̃ electronic spectrum of the β-hydroxyethylperoxy radical: Structure and dynamics

Chen

Just

Codd

et al. 2011

Self Cite

The jet-cooled Ã-X̃ near IR origin band spectra of the G(1)G(2)G(3) conformer of four β-hydroxyethylperoxy isotopologues, β-HEP (HOCH(2)CH(2)OO), β-DHEP (DOCH(2)CH(2)OO), β-HEP-d(4) (HOCD(2)CD(2)OO), and β-DHEP-d(4) (DOCD(2)CD(2)OO), have been recorded by a cavity ringdown spectrometer with a laser source linewidth of ~70 MHz. The spectra of all four isotopologues have been analyzed and successfully simulated with an evolutionary algorithm, confirming the cyclic structure of the molecule responsible for the observed origin band. The analysis also provides experimental Ã and X̃ state rotational constants and the orientation of the transition dipole moment in the inertial axis system; these quantities are compared to results from electronic structure calculations. The observed, broad linewidth (Δν > 2 GHz) is attributed to a shortened lifetime of the Ã state associated with dynamics along the reaction path for hydrogen transfer from the OH to OO group.