Yumin Li

Hong Kong University of Science and Technology

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Joseph S. Francisco

University of Pennsylvania

Jian Zhen Yu

Hong Kong University of Science and Technology

Xu Yu

Shanghai Jiao Tong University

Jaron C. Hansen

Brigham Young University

M. Matti Maricq

Ford Motor Company (United States)

Zhou Yang

Shenzhen Third People’s Hospital

Tzung‐May Fu

Southern University of Science and Technology

Xin Yang

Southern University of Science and Technology

Xinming Wang

Guangzhou Institute of Geochemistry

Kezheng Liao

Hong Kong University of Science and Technology

Cooperative Institutions

Southern University of Science and Technology

Peking University

Hong Kong University of Science and Technology

University of Hong Kong

Purdue University West Lafayette

Harvard University

Chinese Academy of Sciences

California Institute of Technology

Royal Belgian Institute for Space Aeronomy

Jet Propulsion Laboratory

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High level ab initio studies on the excited states of HOCO radical

The Journal of Chemical Physics (2000)

Yumin Li Joseph S. Francisco

The HOCO radical has a ground (X 2A′) and two lowest A″2 excited states that are located using the CCSD(T) level of theory with the cc-pVDZ and cc-pVTZ basis sets. The harmonic frequencies are calculated at the CCSD(T) level of theory with the cc-pVDZ basis set. The vertical excitation energies for the 2 2A′, 3 2A′, 1 2A″, and 2 2A″ states of HOCO are obtained at the MRCI level of theory with the cc-pVTZ and aug-cc-pVTZ basis sets. The first excited state (1 2A″) is calculated to be 70.7 kcal mol−1 above the ground state for trans-HOCO. Comparisons are made between the excited states of HOCO and HCO. It is demonstrated that the HOCO states are not similar to those of HCO.

10.1063/1.1316011

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Citations (34)

NO₂ Quantum Yield from the 248 nm Photodissociation of Peroxynitric Acid (HO₂NO₂)

The Journal of Physical Chemistry A (2000)

Coleen M. Roehl Troy L. Mazely Randall R. Friedl Yumin Li Joseph S. Francisco

Peroxynitric acid (PNA) was photolyzed at 248 nm, and the NO2 photoproduct was detected by laser-induced fluorescence (LIF). The quantum yield for the production of NO2 was determined by comparison with HNO3 photolysis data taken under identical experimental conditions. Measurements made over a range of pressures, flows, and precursor concentrations resulted in an NO2 quantum yield of 0.56 ± 0.17, where the statistical uncertainty is 2 standard deviations. Calculations of potential energy curves for several low-lying singlet and triplet states of PNA are presented. The calculations show that while the singlet excitations occur via an n−π* transition on the NO2 moiety, the dissociative channels forming OH + NO3 and HO2 + NO2 likely occur via predissocation on different surfaces. Excitation energies at the MRCI and CCSD(T) level of theory show that excited states of PNA are not accessible at wavelengths longer than 407 nm (∼3.0 eV).

Quantum yield

10.1021/jp001982x

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An experimental and computational study of the methyl formate radical ultraviolet spectrum

The Journal of Chemical Physics (2000)

Jaron C. Hansen Yumin Li Joseph S. Francisco Joseph J. Szente M. Matti Maricq

Ab initio molecular orbital theory is coupled with laser flash photolysis experiments to study the UV spectrum and absorption cross section of the methyl formate radical. The vertical excitation energies for four of methyl formate radical's excited states are calculated at the MRCI level of theory. In the region between 220 and 340 nm, two electronic transitions are identified to explain the experimental UV spectrum.

Methyl formate

Flash photolysis

Methyl radical

Ultraviolet

10.1063/1.1318741

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Global sources and impacts of absorptive components in atmospheric organic aerosols

Yumin Li

Organic aerosols (OA) are ubiquitous in the troposphere with profound impacts on public health, climate, and the global biogeochemical cycle. However, these environmental impacts of OA remain uncertain because the global sources, abundances, atmospheric evolution, depositions, and radiative properties of OA are not well quantified. In particular, OA are complex mixtures that evolve through atmospheric aging, making them difficult to identify and quantify. Due to measurement limitations, the sources of the absorptive components of OA are not well understood. This thesis aims to quantify the global sources of the absorptive components in atmospheric OA to better assess their climate effects. Biomass burning is a significant source of absorptive OA in the atmosphere. While previous studies...[ Read more ]

Biogeochemical Cycle

Atmospheric Composition

Global climate

10.14711/thesis-991013222943703412

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Ab initio studies on the low-lying excited states of ClO3 and BrO3

The Journal of Chemical Physics (2000)

Yumin Li Joseph S. Francisco

The vertical excitation energies and the transition moments of the ClO3 and BrO3 states, 1 2A1, 1 2A2, 1 2E, and 2 2E, are calculated at the complete active space self-consistent field (CASSCF), multi-reference configuration interaction (MRCI), and complete active space self-consistent field with second-order perturbation correction (CASPT2) levels of theory. The basis sets, cc-pVTZ and aug-cc-pVTZ, are used for ClO3, and cc-pVTZ and TZ2P (2sp) are used for BrO3. The potential energy curves for the states studied are computed at the CASSCF level of theory with the cc-pVTZ basis set. The differences and similarities between the ClO3 and BrO3 states are examined. Results for ClO3 are found to be consistent with recent UV experiment results that are used to characterize the ClO3 radical.

10.1063/1.481501

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Theoretical and Experimental Investigation of the UV Cross Section and Kinetics of the Methyl Formate Peroxy Radical

The Journal of Physical Chemistry A (2003)

Jaron C. Hansen Yumin Li Claudette M. Rosado‐Reyes Joseph S. Francisco Joseph J. Szente

Flash photolysis combined with UV time-resolved spectroscopy has been utilized to investigate the composite UV cross section for methyl formate peroxy (CH3OC(O)O2 and O2CH2OC(O)H) between 210 and 320 nm. The self-reaction rate constant for methyl formate peroxy was measured at 298 K and found to be (2.3 ± 0.7) × 10-11 cm3 molecule-1 s-1. Evidence is reported for the production of OH radical and CH2O from the decomposition of the activated methyl formate peroxy radical produced by the addition of O2 to methyl formate radical, and for the formation of ClO from the Cl + peroxy reaction. High level ab initio calculations were performed to explore the methyl formate oxidation mechanism as well as to assign the experimentally observed UV spectrum. The calculated UV spectrum band center is found to be within 10% of the experimentally determined methyl formate peroxy spectrum. High-resolution IR detection of the CH2O fragment was used to probe the branching ratio for unimolecular dissociation relative to collisional stabilization of the activated methyl formate peroxy radical as a function of pressure. The dissociation kinetics is described using a modified Lindemann mechanism.

Methyl formate

Methyl radical

Ethyl formate

Flash photolysis

Methyl group

10.1021/jp021180x

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Ab initio study of the electronic spectrum of peroxyacetyl nitrate

The Journal of Chemical Physics (2004)

Joseph S. Francisco Yumin Li

A theoretical study of the ground and excited states of peroxyacetyl nitrate (PAN), CH3C(O)OONO2, has been carried out using high level ab initio molecular orbital methods. The ground state geometry and vibrational frequencies are calculated using the coupled-cluster method. The vertical excitation energies for the lowest three excited states are calculated using the complete active space self-consistent field method along with the multireference internally contracted configuration interaction method. These results are compared with vertical excitation energies calculated with the coupled cluster equation of motion method. The calculation provides relevant insight into the origin of PAN absorption in the UV wavelength region from 200 to 300 nm. The nature of the electron transitions for these excited states is discussed.

Multireference configuration interaction

Coupled cluster

Peroxyacetyl nitrate

10.1063/1.1786581

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Transport paths and vertical exchange characteristics of haze pollution in Southern China

The Science of The Total Environment (2018)

Tingyuan Li Xuejiao Deng Yumin Li Yushan Song L.Y. Li

Haze

HYSPLIT

10.1016/j.scitotenv.2017.12.235

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Citations (46)

Temperature-Dependent Evaporative Anthropogenic VOC Emissions Significantly Exacerbate Regional Ozone Pollution

Environmental Science & Technology (2024)

Wenlu Wu Tzung‐May Fu S. R. Arnold Dominick V. Spracklen Aoxing Zhang

The evaporative emissions of anthropogenic volatile organic compounds (AVOCs) are sensitive to ambient temperature. This sensitivity forms an air pollution-meteorology connection that has not been assessed on a regional scale. We parametrized the temperature dependence of evaporative AVOC fluxes in a regional air quality model and evaluated the impacts on surface ozone in the Beijing–Tianjin–Hebei (BTH) area of China during the summer of 2017. The temperature dependency of AVOC emissions drove an enhanced simulated ozone-temperature sensitivity of 1.0 to 1.8 μg m–3 K–1, comparable to the simulated ozone-temperature sensitivity driven by the temperature dependency of biogenic VOC emissions (1.7 to 2.4 μg m–3 K–1). Ozone enhancements driven by temperature-induced AVOC increases were localized to their point of emission and were relatively more important in urban areas than in rural regions. The inclusion of the temperature-dependent AVOC emissions in our model improved the simulated ozone-temperature sensitivities on days of ozone exceedance. Our results demonstrated the importance of temperature-dependent AVOC emissions on surface ozone pollution and its heretofore unrepresented role in air pollution–meteorology interactions.

10.1021/acs.est.3c09122

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Citations (16)

Location of the first excited states of fluorinated ethers, E143a (CH3OCF3), E134 (CHF2OCHF2), and E125 (CHF2OCF3)

Chemical Physics Letters (1999)

David A. Good Yumin Li Joseph S. Francisco

Dimethyl ether

10.1016/s0009-2614(99)01032-5

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Citations (8)