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Goodwin MJ, Dickenson JC, Ripak A, Deetz AM, McCarthy JS, Meyer GJ, Troian-Gautier L. Factors that Impact Photochemical Cage Escape Yields. Chem Rev 2024; 124:7379-7464. [PMID: 38743869 DOI: 10.1021/acs.chemrev.3c00930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
The utilization of visible light to mediate chemical reactions in fluid solutions has applications that range from solar fuel production to medicine and organic synthesis. These reactions are typically initiated by electron transfer between a photoexcited dye molecule (a photosensitizer) and a redox-active quencher to yield radical pairs that are intimately associated within a solvent cage. Many of these radicals undergo rapid thermodynamically favored "geminate" recombination and do not diffuse out of the solvent cage that surrounds them. Those that do escape the cage are useful reagents that may undergo subsequent reactions important to the above-mentioned applications. The cage escape process and the factors that determine the yields remain poorly understood despite decades of research motivated by their practical and fundamental importance. Herein, state-of-the-art research on light-induced electron transfer and cage escape that has appeared since the seminal 1972 review by J. P. Lorand entitled "The Cage Effect" is reviewed. This review also provides some background for those new to the field and discusses the cage escape process of both homolytic bond photodissociation and bimolecular light induced electron transfer reactions. The review concludes with some key goals and directions for future research that promise to elevate this very vibrant field to even greater heights.
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Affiliation(s)
- Matthew J Goodwin
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - John C Dickenson
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Alexia Ripak
- Université catholique de Louvain (UCLouvain), Institut de la Matière Condensée et des Nanosciences (IMCN), Molecular Chemistry, Materials and Catalysis (MOST), Place Louis Pasteur 1, bte L4.01.02, 1348 Louvain-la-Neuve, Belgium
| | - Alexander M Deetz
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Jackson S McCarthy
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Gerald J Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Ludovic Troian-Gautier
- Université catholique de Louvain (UCLouvain), Institut de la Matière Condensée et des Nanosciences (IMCN), Molecular Chemistry, Materials and Catalysis (MOST), Place Louis Pasteur 1, bte L4.01.02, 1348 Louvain-la-Neuve, Belgium
- Wel Research Institute, Avenue Pasteur 6, 1300 Wavre, Belgium
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2
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Molecular Dynamics Study of the Photodissociation of ICN in Ethanol: Effect of Solvent Polarity. J SOLUTION CHEM 2021. [DOI: 10.1007/s10953-021-01094-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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3
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Finlayson-Pitts BJ. Introductory lecture: atmospheric chemistry in the Anthropocene. Faraday Discuss 2017; 200:11-58. [DOI: 10.1039/c7fd00161d] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The term “Anthropocene” was coined by Professor Paul Crutzen in 2000 to describe an unprecedented era in which anthropogenic activities are impacting planet Earth on a global scale. Greatly increased emissions into the atmosphere, reflecting the advent of the Industrial Revolution, have caused significant changes in both the lower and upper atmosphere. Atmospheric reactions of the anthropogenic emissions and of those with biogenic compounds have significant impacts on human health, visibility, climate and weather. Two activities that have had particularly large impacts on the troposphere are fossil fuel combustion and agriculture, both associated with a burgeoning population. Emissions are also changing due to alterations in land use. This paper describes some of the tropospheric chemistry associated with the Anthropocene, with emphasis on areas having large uncertainties. These include heterogeneous chemistry such as those of oxides of nitrogen and the neonicotinoid pesticides, reactions at liquid interfaces, organic oxidations and particle formation, the role of sulfur compounds in the Anthropocene and biogenic–anthropogenic interactions. A clear and quantitative understanding of the connections between emissions, reactions, deposition and atmospheric composition is central to developing appropriate cost-effective strategies for minimizing the impacts of anthropogenic activities. The evolving nature of emissions in the Anthropocene places atmospheric chemistry at the fulcrum of determining human health and welfare in the future.
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4
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Translational, rotational and vibrational relaxation dynamics of a solute molecule in a non-interacting solvent. Nat Chem 2016; 8:1042-1046. [DOI: 10.1038/nchem.2570] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2016] [Accepted: 06/10/2016] [Indexed: 11/08/2022]
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Coulter P, Grubb MP, Koyama D, Sazanovich IV, Greetham GM, Orr-Ewing AJ. Recombination, Solvation and Reaction of CN Radicals Following Ultraviolet Photolysis of ICN in Organic Solvents. J Phys Chem A 2015; 119:12911-23. [DOI: 10.1021/acs.jpca.5b10716] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Philip Coulter
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K
| | - Michael P. Grubb
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K
| | - Daisuke Koyama
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K
| | - Igor V. Sazanovich
- Central
Laser Facility, Research Complex at Harwell, Science and Technology
Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot,
Oxfordshire, OX11 0QX, U.K
| | - Gregory M. Greetham
- Central
Laser Facility, Research Complex at Harwell, Science and Technology
Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot,
Oxfordshire, OX11 0QX, U.K
| | - Andrew J. Orr-Ewing
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K
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6
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Richards-Henderson NK, Anderson C, Anastasio C, Finlayson-Pitts BJ. The effect of cations on NO2 production from the photolysis of aqueous thin water films of nitrate salts. Phys Chem Chem Phys 2015; 17:32211-8. [DOI: 10.1039/c5cp05325k] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Cations are shown to enhance nitrate photochemistry by changing the concentrations of nitrate ions in the interface region.
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Affiliation(s)
| | | | - Cort Anastasio
- Department of Land
- Air and Water Resources
- University of California – Davis
- Davis
- USA
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7
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Zhang Y, Oliver TAA, Das S, Roy A, Ashfold MNR, Bradforth SE. Exploring the Energy Disposal Immediately After Bond-Breaking in Solution: The Wavelength-Dependent Excited State Dissociation Pathways of para-Methylthiophenol. J Phys Chem A 2013; 117:12125-37. [DOI: 10.1021/jp405160n] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yuyuan Zhang
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | - Thomas A. A. Oliver
- School of Chemistry, Cantocks Close, University of Bristol, Bristol BS8 1TS, U.K
| | - Saptaparna Das
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | - Anirban Roy
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | | | - Stephen E. Bradforth
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
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8
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Zhang Y, Oliver TAA, Ashfold MNR, Bradforth SE. Contrasting the excited state reaction pathways of phenol and para-methylthiophenol in the gas and liquid phases. Faraday Discuss 2013; 157:141-63; discussion 243-84. [PMID: 23230767 DOI: 10.1039/c2fd20043k] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
To explore how the solvent influences primary aspects of bond breaking, the gas and solution phase photochemistries of phenol and ofpara-methylthiophenol are directly compared using, respectively, H (Rydberg) atom photofragment translation spectroscopy and femtosecond transient absorption spectroscopy. Approaches are demonstrated that allow explicit comparisons of the nascent product energy disposals and dissociation mechanisms in the two phases. It is found, at least for the case of the weakly perturbing cyclohexane environment, that most aspects of the primary reaction dynamics of the isolated molecule are reproduced in solution. Specifically, in the gas phase, both molecules can undergo fast X-H (X = O, S) bond dissociation upon excitation with short wavelengths (193 < lambda(pump) < 216 nm), following population of the dissociative S2 (1 1(pi sigma*)) state. Product electronic branching, vibrational and translational energy disposals are determined. Photolysis of phenol and para-methylthiophenol in solution at 200 nm results in formation of vibrationally excited radicals on a timescale shorter than 200 fs. Excitation of para-methylthiophenol at 267 nm reaches close to the S1 (1 1(pipi*))/S2 (11(pi sigma*)) conical intersection (CI): ultrafast dissociation is observed in both the isolated and solution systems-again indicating direct dissociation on the S2 potential energy surface. Comparing results for this precursor at different excitation energies, the extent of geminate recombination and the derived H-atom ejection lengths in the condensed phase photolyses are in qualitative agreement with the translational energy release measured in the gas phase studies. Conversely, excitation of phenol at 267 nm prepares the system in its S1 state at an energy well below its S1/S2 CI; the slow O-H bond fission inferred in the gas phase experiments is observed directly in the time-resolved studies in cyclohexane solution via the appearance of phenoxyl radical absorption after -1 ns, with only S1 excited state absorption discernible at earlier delay times. The slow O-H bond fission in solution provides additional evidence for a tunnelling dissociation mechanism, where the H atom tunnels beneath the lower diabats of the S2/S1 CI. Finally, the photodissociation of phenol clusters in solution is considered, where evidence is presented that the O-H dissociation coordinate is impeded in H-bonded dimers.
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Affiliation(s)
- Yuyuan Zhang
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
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Moussa SG, Stern AC, Raff JD, Dilbeck CW, Tobias DJ, Finlayson-Pitts BJ. Experimental and theoretical studies of the interaction of gas phase nitric acid and water with a self-assembled monolayer. Phys Chem Chem Phys 2013; 15:448-58. [DOI: 10.1039/c2cp42405c] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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10
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Petersen J, Henriksen NE, Møller KB. Validity of the Bersohn–Zewail model beyond justification. Chem Phys Lett 2012. [DOI: 10.1016/j.cplett.2012.05.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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11
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Cazade PA, Huang J, Yosa J, Szymczak JJ, Meuwly M. Atomistic simulations of reactive processes in the gas- and condensed-phase. INT REV PHYS CHEM 2012. [DOI: 10.1080/0144235x.2012.694694] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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12
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Miller EM, Sheps L, Lu YJ, Case AS, McCoy AB, Lineberger WC. New view of the ICN A continuum using photoelectron spectroscopy of ICN-. J Chem Phys 2012; 136:044313. [PMID: 22299877 DOI: 10.1063/1.3679170] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Negative-ion photoelectron spectroscopy of ICN(-) (X̃ (2)Σ(+)) reveals transitions to the ground electronic state (X̃ (1)Σ(+)) of ICN as well as the first five excited states ((3)Π(2), (3)Π(1), Π(0(-) ) (3), Π(0(+) ) (3), and (1)Π(1)) that make up the ICN A continuum. By starting from the equilibrium geometry of the anion, photoelectron spectroscopy characterizes the electronic structure of ICN at an elongated I-C bond length of 2.65 Å. Because of this bond elongation, the lowest three excited states of ICN ((3)Π(2), (3)Π(1), and Π(0(-) ) (3)) are resolved for the first time in the photoelectron spectrum. In addition, the spectrum has a structured peak that arises from the frequently studied conical intersection between the Π(0(+) ) (3) and (1)Π(1) states. The assignment of the spectrum is aided by MR-SO-CISD calculations of the potential energy surfaces for the anion and neutral ICN electronic states, along with calculations of the vibrational levels supported by these states. Through thermochemical cycles involving spectrally narrow transitions to the excited states of ICN, we determine the electron affinity, EA(ICN), to be 1.34(5) (+0.04∕-0.02) eV and the anion dissociation energy, D(0)(X̃ (2)Σ(+) I-CN(-)), to be 0.83 (+0.04/-0.02) eV.
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Affiliation(s)
- Elisa M Miller
- JILA, Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309, USA
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13
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Lutz S, Meuwly M. Photodissociation Dynamics of ClCN at Different Wavelengths. Chemphyschem 2011; 13:305-13. [DOI: 10.1002/cphc.201100575] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2011] [Indexed: 11/07/2022]
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14
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Richards NK, Wingen LM, Callahan KM, Nishino N, Kleinman MT, Tobias DJ, Finlayson-Pitts BJ. Nitrate Ion Photolysis in Thin Water Films in the Presence of Bromide Ions. J Phys Chem A 2011; 115:5810-21. [DOI: 10.1021/jp109560j] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Nicole K. Richards
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Lisa M. Wingen
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Karen M. Callahan
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Noriko Nishino
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Michael T. Kleinman
- Department of Medicine, University of California, Irvine, California 92697-1825, United States
| | - Douglas J. Tobias
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
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15
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Rivera CA, Winter N, Harper RV, Benjamin I, Bradforth SE. The dynamical role of solvent on the ICN photodissociation reaction: connecting experimental observables directly with molecular dynamics simulations. Phys Chem Chem Phys 2011; 13:8269-83. [DOI: 10.1039/c1cp20252a] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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16
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Oliver TAA, Zhang Y, Ashfold MNR, Bradforth SE. Linking photochemistry in the gas and solution phase: S–H bond fission in p-methylthiophenol following UV photoexcitation. Faraday Discuss 2011; 150:439-58; discussion 505-32. [DOI: 10.1039/c0fd00031k] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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17
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Wick CD, Dang LX. The behavior of NaOH at the air-water interface: A computational study. J Chem Phys 2010; 133:024705. [DOI: 10.1063/1.3455332] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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18
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Wick CD, Dang LX. Computational investigation of the influence of organic-aqueous interfaces on NaCl dissociation dynamics. J Chem Phys 2010; 132:044702. [DOI: 10.1063/1.3299279] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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19
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Johnson ML, Benjamin I. Photodissociation of ICN at the Water/Chloroform Interface. J Phys Chem A 2009; 113:7403-11. [DOI: 10.1021/jp900153j] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Mindy L. Johnson
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064
| | - Ilan Benjamin
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064
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21
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Finlayson-Pitts BJ. Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols. Phys Chem Chem Phys 2009; 11:7760-79. [DOI: 10.1039/b906540g] [Citation(s) in RCA: 203] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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22
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Tapavicza E, Tavernelli I, Rothlisberger U, Filippi C, Casida ME. Mixed time-dependent density-functional theory/classical trajectory surface hopping study of oxirane photochemistry. J Chem Phys 2008; 129:124108. [DOI: 10.1063/1.2978380] [Citation(s) in RCA: 169] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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23
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Wingen LM, Moskun AC, Johnson SN, Thomas JL, Roeselová M, Tobias DJ, Kleinman MT, Finlayson-Pitts BJ. Enhanced surface photochemistry in chloride–nitrate ion mixtures. Phys Chem Chem Phys 2008; 10:5668-77. [DOI: 10.1039/b806613b] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Tao G, Stratt RM. The molecular origins of nonlinear response in solute energy relaxation: The example of high-energy rotational relaxation. J Chem Phys 2006; 125:114501. [PMID: 16999484 DOI: 10.1063/1.2336780] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
A key step in solution-phase chemical reactions is often the removal of excess internal energy from the product. Yet, the way one typically studies this process is to follow the relaxation of a solute that has been excited into some distribution of excited states quite different from that produced by any reaction of interest. That the effects of these different excitations can frequently be ignored is a consequence of the near universality of linear-response behavior, the idea that relaxation dynamics is determined by the solvent fluctuations (which may not be all that different for different kinds of solute excitation). Nonetheless, there are some clear examples of linear-response breakdowns seen in solute relaxation, including a recent theoretical and experimental study of rapidly rotating diatomics in liquids. In this paper we use this rotational relaxation example to carry out a theoretical exploration of the conditions that lead to linear-response failure. Some features common to all of the linear-response breakdowns studied to date, including our example, are that the initial solute preparation is far from equilibrium, that the subsequent relaxation promotes a significant rearrangement of the liquid structure, and that the nonequilibrium response is nonstationary. However, we show that none of these phenomena is enough to guarantee a nonlinear response. One also needs a sufficient separation between the solute time scale and that of the solvent geometry evolution. We illustrate these points by demonstrating precisely how our relaxation rate is tied to our liquid-structural evolution, how we can quantitatively account for the initial nonstationarity of our effective rotational friction, and how one can tune our rotational relaxation into and out of linear response.
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Affiliation(s)
- Guohua Tao
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
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25
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Benjamin I. Theoretical Studies of Solute Vibrational Energy Relaxation at Liquid Interfaces. J Phys Chem B 2006; 110:9375-82. [PMID: 16686479 DOI: 10.1021/jp056420y] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Recent advances in the theoretical understanding of solute vibrational energy relaxation at liquid interfaces and surfaces are described. Non-equilibrium molecular dynamics simulations of the relaxation of an initially excited solute molecule are combined with equilibrium force autocorrelation calculations to gain insight into the factors that influence the vibrational relaxation rate. Diatomic and triatomic nonpolar, polar, and ionic solute molecules adsorbed at the liquid/vapor interface of several liquids as well as at the water/CCl(4) liquid/liquid interface are considered. In general, the vibrational relaxation rate is significantly slower (a factor of 3 to 4) at the liquid/vapor and liquid/liquid interface than in the bulk due to the reduced density, which gives rise to a reduced contribution of the repulsive solvent-solute forces on the vibrational mode. The surface effects on the ionic solutes are much smaller (50% or less slower relaxation relative to the bulk). This is due to the fact that ionic solutes at the interface are able to keep part of their solvation shell to a degree that depends on their size. Thus, a significant portion of the repulsive forces is maintained. A high degree of correlation is found between the peak height of the solvent-solute radial distribution function and the vibrational relaxation rate. The relaxation rate at the liquid/liquid interface strongly depends on the location of the solute across the interface and correlates with the change in the density and polarity profile of the interface.
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Affiliation(s)
- Ilan Benjamin
- Department of Chemistry and Biochemistry, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
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Nissenson P, Knox CJH, Finlayson-Pitts BJ, Phillips LF, Dabdub D. Enhanced photolysis in aerosols: evidence for important surface effects. Phys Chem Chem Phys 2006; 8:4700-10. [PMID: 17047769 DOI: 10.1039/b609219e] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
While there is increasing evidence for unique chemical reactions at interfaces, there are fewer data on photochemistry at liquid-vapor junctions. This paper reports a comparison of the photolysis of molybdenum hexacarbonyl, Mo(CO)(6), in 1-decene either as liquid droplets or in bulk-liquid solutions. Mo(CO)(6) photolysis is faster by at least three orders of magnitude in the aerosols than in bulk-liquids. Two possible sources of this enhancement are considered: (1) increased light intensity due to either Morphology-Dependent Resonances (MDRs) in the spherical aerosol particles and/or to increased pathlengths for light inside the droplet due to refraction, which are termed physical effects in this paper; and (2) interface effects such as an incomplete solvent-cage at the gas-liquid boundary and/or enhanced interfacial concentrations of Mo(CO)(6), which are termed chemical effects. Quantitative calculations of the first possibility were carried out in which the light intensity distribution in the droplets averaged over 215-360 nm was obtained for 1-decene droplets. Calculations show that the average increase in light intensity over the entire droplet is 106%, with an average increase of 51% at the interface. These increases are much smaller than the observed increase in the apparent photolysis rate of droplets compared to the bulk. Thus, chemical effects, i.e., a decreased solvent-cage effect at the interface and/or enhancement in the surface concentration of Mo(CO)(6), are most likely responsible for the dramatic increase in the photolysis rate. Similar calculations were also carried out for broadband (290-600 nm) solar irradiation of water droplets, relevant to atmospheric conditions. These calculations show that, in agreement with previous calculations by Mayer and Madronich [B. Mayer and S. Madronich, Atmos. Chem. Phys., 2004, 4, 2241] MDRs produce only a moderate average intensity enhancement relative to the corresponding bulk-liquid slabs when averaged over a range of wavelengths characteristic of solar radiation at the Earth's surface. However, as in the case of Mo(CO)(6) in 1-decene, chemical effects may play a role in enhanced photochemistry at the aerosol-air interface for airborne particles.
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Affiliation(s)
- Paul Nissenson
- Department of Mechanical and Aerospace Engineering, University of California, Irvine, California 92697-3975, USA
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