Physical Chemistry Chemical Physics, Год журнала: 2024, Номер unknown
Опубликована: Дек. 30, 2024
The hydrogen shift reaction occurs on the singlet potential energy surface.
Язык: Английский
Proceedings of the National Academy of Sciences, Год журнала: 2024, Номер 121(16)
Опубликована: Апрель 11, 2024
The oxidation of cycloalkanes is important in the combustion transportation fuels and atmospheric secondary organic aerosol formation. A transient carbon-centered radical intermediate (•QOOH) cyclohexane identified through its infrared fingerprint time- energy-resolved unimolecular dissociation dynamics to hydroxyl (OH) bicyclic ether products. Although cyclohexyl ring structure leads three nearly degenerate •QOOH isomers (β-, γ-, δ-QOOH), their transition state (TS) barriers OH products are predicted differ considerably. Selective characterization β-QOOH isomer achieved at excitation energies associated with lowest TS barrier, resulting rapid decay that detected. benchmarking approach employed for calculation high-accuracy stationary point energies, particular barriers, (C 6 H 11 O 2 ), building on higher-level reference calculations smaller ethane 5 ) system. isomer-specific validated by comparison experimental product appearance rates computed statistical microcanonical rates, including significant heavy-atom tunneling, vicinity barrier. Master-equation modeling utilized extend results thermal rate constants temperatures pressures relevant combustion.
Язык: Английский
Процитировано
6
Chemical Engineering Journal, Год журнала: 2025, Номер 507, С. 160459 - 160459
Опубликована: Фев. 11, 2025
Язык: Английский
Процитировано
0
The Journal of Physical Chemistry A, Год журнала: 2025, Номер unknown
Опубликована: Март 20, 2025
The UV photodissociation dynamics of three organic hydroperoxides (ROOH, R = tert-butyl, cyclopentyl, and cyclohexyl) are examined experimentally at 282 nm utilizing velocity map imaging the OH X2Π3/2 (v″ 0, J″) products. systems have similar O–O bond dissociation energies based on W1BD calculations thus energy release to In each case, experimental total kinetic (TKER) distributions bimodal, composed narrow low broad high TKER components extending over available energy. associated angular X2Π products isotropic, differing dramatically from those predicted for direct photodissociation. Complementary theoretical relaxed potential profile ROOH along steeply repulsive excited state (S1) leading RO + Low CCOO torsional barriers pathway enable recoil in many different directions, yielding isotropic distributions. Simple models suggest that component arises internal conversion ground (S0) potential, a common product asymptote. A simple impulsive model captures some aspects but neglects significant geometric changes alkyl substituent product. This study provides new insight into solar photolysis regeneration radicals atmospheric oxidation cycles.
Язык: Английский
Процитировано
0
The Journal of Physical Chemistry A, Год журнала: 2024, Номер 128(42), С. 9240 - 9250
Опубликована: Окт. 15, 2024
A transient carbon-centered hydroperoxyalkyl intermediate (•QOOH) in the oxidation of cyclopentane is identified by IR action spectroscopy with time-resolved unimolecular decay to hydroxyl (OH) radical products that are detected UV laser-induced fluorescence. Two nearly degenerate •QOOH isomers, β- and γ-QOOH, generated H atom abstraction cyclopentyl hydroperoxide precursor. Fundamental first overtone OH stretch transitions combination bands observed compared anharmonic frequencies computed second-order vibrational perturbation theory. An transition also for a conformer arising from torsion about low-energy CCOO barrier. Definitive identification β-QOOH isomer relies on its significantly lower state (TS) barrier products, which results rapid near unity branching products. benchmarking approach utilized compute high-accuracy stationary point energies, most importantly TS barriers, (C
Язык: Английский
Процитировано
2
The Journal of Chemical Physics, Год журнала: 2024, Номер 161(3)
Опубликована: Июль 15, 2024
Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated the laboratory by H-atom abstraction from corresponding ring sites of cyclohexyl hydroperoxide (CHHP) precursor. IR spectral features jet-cooled stabilized observed 3590 7010 cm−1 (∼10–20 kcal mol−1) at energies vicinity transition state (TS) barrier leading OH that detected ultraviolet laser-induced fluorescence. experimental approach affords selective detection β-QOOH, arising its significantly lower TS products compared γ δ results rapid unimolecular decay near unity branching products. spectrum β-QOOH includes fundamental overtone stretch transitions, CH combination bands involving or with frequency modes. assignment guided anharmonic frequencies intensities computed using second-order vibrational perturbation theory. (2νOH) shifted only a few wavenumbers for CHHP precursor, yet they readily distinguished their prompt vs slow dissociation rates
Язык: Английский
Процитировано
1
Physical Chemistry Chemical Physics, Год журнала: 2024, Номер unknown
Опубликована: Дек. 30, 2024
The hydrogen shift reaction occurs on the singlet potential energy surface.
Язык: Английский
Процитировано
0