Atmospheric Chemistry of CF₃CF₂CHO: Absorption Cross Sections in the UV and IR Regions, Photolysis at 308 nm, and Gas-Phase Reaction with OH Radicals (<i>T</i> = 263–358 K)

The relative importance in the atmosphere of UV photolysis of perfluoropropionaldehyde, CF₃CF₂CHO, and reaction with hydroxyl (OH) radicals has been investigated in this work. First, the forbidden n → π* transition of the carbonyl chromophore was characterized between 230 and 380 nm as a function of temperature (269–298 K) and UV absorption cross sections, σ_λ, were determined in those ranges. In addition, IR absorption cross sections were determined between 4000 and 500 cm^–1. Pulsed laser photolysis (PLP) of CF₃CF₂CHO coupled to Fourier transform infrared (FTIR) was employed to determine the overall photolysis quantum yield, Φ_λ, at 308 nm and 298 K. Φ_λ=308 nm was pressure dependent, ranging from (0.94 ± 0.14) at 75 Torr to (0.30 ± 0.01) at 760 Torr. This dependence is characterized by the Stern–Volmer parameters Φ_λ=308 nm⁰ = (1.19 ± 0.34) and <i>K</i>_SV = (1.22 ± 0.52) × 10^–19 cm³ molecule^–1. End products of the photodissociation of CF₃CF₂CHO were measured and quantified by FTIR spectroscopy. Furthermore, the rate coefficients for the OH + CF₃CF₂CHO reaction, <i>k</i>₁, were determined as a function of temperature (<i>T</i> = 263–358 K) by PLP-LIF. At room temperature the rate coefficient is <i>k</i>₁(<i>T</i> = 298 K) = (5.57 ± 0.07) × 10^–13 cm³ molecule^–1 s^–1, whereas the temperature dependence is described by <i>k</i>₁(<i>T</i>) = (2.56 ± 0.32) × 10^–12 exp{−(458 ± 36)/<i>T</i>} cm³ molecule^–1 s^–1. On the basis of our results, photolysis of CF₃CF₂CHO in the actinic region could be an important removal process for CF₃CF₂CHO in the atmosphere. The formation of the primary products in the UV photolysis of CF₃CF₂CHO is also discussed

Atmospheric Chemistry of CF₃CF₂CHO: Absorption Cross Sections in the UV and IR Regions, Photolysis at 308 nm, and Gas-Phase Reaction with OH Radicals (<i>T</i> = 263–358 K)

The relative importance in the atmosphere of UV photolysis of perfluoropropionaldehyde, CF₃CF₂CHO, and reaction with hydroxyl (OH) radicals has been investigated in this work. First, the forbidden n → π* transition of the carbonyl chromophore was characterized between 230 and 380 nm as a function of temperature (269–298 K) and UV absorption cross sections, σ_λ, were determined in those ranges. In addition, IR absorption cross sections were determined between 4000 and 500 cm^–1. Pulsed laser photolysis (PLP) of CF₃CF₂CHO coupled to Fourier transform infrared (FTIR) was employed to determine the overall photolysis quantum yield, Φ_λ, at 308 nm and 298 K. Φ_λ=308 nm was pressure dependent, ranging from (0.94 ± 0.14) at 75 Torr to (0.30 ± 0.01) at 760 Torr. This dependence is characterized by the Stern–Volmer parameters Φ_λ=308 nm⁰ = (1.19 ± 0.34) and <i>K</i>_SV = (1.22 ± 0.52) × 10^–19 cm³ molecule^–1. End products of the photodissociation of CF₃CF₂CHO were measured and quantified by FTIR spectroscopy. Furthermore, the rate coefficients for the OH + CF₃CF₂CHO reaction, <i>k</i>₁, were determined as a function of temperature (<i>T</i> = 263–358 K) by PLP-LIF. At room temperature the rate coefficient is <i>k</i>₁(<i>T</i> = 298 K) = (5.57 ± 0.07) × 10^–13 cm³ molecule^–1 s^–1, whereas the temperature dependence is described by <i>k</i>₁(<i>T</i>) = (2.56 ± 0.32) × 10^–12 exp{−(458 ± 36)/<i>T</i>} cm³ molecule^–1 s^–1. On the basis of our results, photolysis of CF₃CF₂CHO in the actinic region could be an important removal process for CF₃CF₂CHO in the atmosphere. The formation of the primary products in the UV photolysis of CF₃CF₂CHO is also discussed

Atmospheric Chemistry of CF₃CF₂CHO: Absorption Cross Sections in the UV and IR Regions, Photolysis at 308 nm, and Gas-Phase Reaction with OH Radicals (<i>T</i> = 263–358 K)

The relative importance in the atmosphere of UV photolysis of perfluoropropionaldehyde, CF₃CF₂CHO, and reaction with hydroxyl (OH) radicals has been investigated in this work. First, the forbidden n → π* transition of the carbonyl chromophore was characterized between 230 and 380 nm as a function of temperature (269–298 K) and UV absorption cross sections, σ_λ, were determined in those ranges. In addition, IR absorption cross sections were determined between 4000 and 500 cm^–1. Pulsed laser photolysis (PLP) of CF₃CF₂CHO coupled to Fourier transform infrared (FTIR) was employed to determine the overall photolysis quantum yield, Φ_λ, at 308 nm and 298 K. Φ_λ=308 nm was pressure dependent, ranging from (0.94 ± 0.14) at 75 Torr to (0.30 ± 0.01) at 760 Torr. This dependence is characterized by the Stern–Volmer parameters Φ_λ=308 nm⁰ = (1.19 ± 0.34) and <i>K</i>_SV = (1.22 ± 0.52) × 10^–19 cm³ molecule^–1. End products of the photodissociation of CF₃CF₂CHO were measured and quantified by FTIR spectroscopy. Furthermore, the rate coefficients for the OH + CF₃CF₂CHO reaction, <i>k</i>₁, were determined as a function of temperature (<i>T</i> = 263–358 K) by PLP-LIF. At room temperature the rate coefficient is <i>k</i>₁(<i>T</i> = 298 K) = (5.57 ± 0.07) × 10^–13 cm³ molecule^–1 s^–1, whereas the temperature dependence is described by <i>k</i>₁(<i>T</i>) = (2.56 ± 0.32) × 10^–12 exp{−(458 ± 36)/<i>T</i>} cm³ molecule^–1 s^–1. On the basis of our results, photolysis of CF₃CF₂CHO in the actinic region could be an important removal process for CF₃CF₂CHO in the atmosphere. The formation of the primary products in the UV photolysis of CF₃CF₂CHO is also discussed

Mechanistic and Kinetic Study on the Reactions of Coumaric Acids with Reactive Oxygen Species: A DFT Approach

The mechanism and kinetics of reactions between coumaric acids and a series of reactive oxygen species (^•OX) was studied through the density functional theory (DFT). H atom abstraction from −OH and −COOH groups and addition to the nonaromatic double bond were the most representative reaction pathways chosen for which free energy barriers and rate constants were calculated within the transition state theory (TST) framework. From these calculations, it was estimated that ^•OH > ^•OCH₃ > ^•OOH > ^•OOCH₃ is the order of reactivity of ^•OX with any coumaric acid. The highest rate constant was estimated for <i>p</i>-coumaric acid + ^•OH reaction, whereas the rest of the ^•OX species are more reactive with <i>o</i>-coumaric acid. On the basis of the calculated rate constants, H abstraction from a −OH group should be the main mechanism for the reactions involving ^•OCH₃, ^•OOH, and ^•OOCH₃ radicals. Nevertheless, the addition mechanism, which sometimes is not considered in theoretical studies on reactions of phenolic compounds with electrophilic species, could play a relevant role in the global mechanism of coumaric acid + ^•OH reactions

Atmospheric Chemistry of <i>E</i>- and <i>Z</i>‑CF₃CHCHF (HFO-1234ze): OH Reaction Kinetics as a Function of Temperature and UV and IR Absorption Cross Sections

We report here the rate coefficients for the OH reactions (<i>k</i>_OH) with <i>E</i>-CF₃CHCHF and <i>Z</i>-CF₃CHCHF, potential substitutes of HFC-134a, as a function of temperature (263–358 K) and pressure (45–300 Torr) by pulsed laser photolysis coupled to laser-induced fluorescence techniques. For the <i>E</i>-isomer, the existing discrepancy among previous results on the <i>T</i> dependence of <i>k</i>_OH needs to be elucidated. For the <i>Z</i>-isomer, this work constitutes the first absolute determination of <i>k</i>_OH. No pressure dependence of <i>k</i>_OH was observed, while <i>k</i>_OH exhibits a non-Arrhenius behavior: <i>k</i>_OH(<i>E</i>) = (7.6±0.2)×10−13(T298)2.44⁡exp(666±10T) and <i>k</i>_OH(<i>Z</i>) = (1.4±0.1)×10−13(T298)1.91⁡exp(640±13T) cm³ molecule^–1 s^–1, where uncertainties are 2σ. UV absorption cross sections, σ_λ, are reported for the first time. From σ_λ and considering a photolysis quantum yield of 1, an upper limit for the photolysis rate coefficients and lifetimes due to this process in the troposphere are estimated: 3 × 10^–8 s^–1 and >1 year for the <i>E</i>-isomer and 2 × 10^–7 s^–1 and >2 months for <i>Z</i>-CF₃CHCHF, respectively. Under these conditions, the overall estimated tropospheric lifetimes are 15 days (for the <i>E</i>-isomer) and 8 days (for the <i>Z</i>-isomer), the major degradation pathway being the OH reaction, with a contribution of the photolytic pathway of less than 3% (for <i>E</i>) and 13% (for <i>Z</i>). IR absorption cross sections were determined both experimentally (500–4000 cm^–1) and theoretically (0–2000 cm^–1). From the theoretical IR measurements, it is concluded that the contribution of the 0–500 cm^–1 region to the total integrated cross sections is appreciable for the <i>E</i>-isomer (9%) but almost negligible for the <i>Z</i>-isomer (0.5%). Nevertheless, the impact on their radiative efficiency and global warming potential is negligible

Laboratory Studies of CHF₂CF₂CH₂OH and CF₃CF₂CH₂OH: UV and IR Absorption Cross Sections and OH Rate Coefficients between 263 and 358 K

Fluorinated alcohols, such as 2,2,3,3-tetrafluoropropanol (TFPO, CHF₂CF₂CH₂OH) and 2,2,3,3,3-pentafluoropropanol (PFPO, CF₃CF₂CH₂OH), can be potential replacements of hydrofluorocarbons with large global warming potentials, GWPs. IR absorption cross sections for TFPO and PFPO were determined between 4000 and 500 cm^–1 at 298 K. Integrated absorption cross sections (<i>S</i>_int, base <i>e</i>) in the 4000–600 cm^–1 range are (1.92 ± 0.34) × 10^–16 cm² molecule^–1 cm^–1 and (2.05 ± 0.50) × 10^–16 cm² molecule^–1 cm^–1 for TFPO and PFPO, respectively. Uncertainties are at a 95% confidence level. Ultraviolet absorption spectra were also recorded between 195 and 360 nm at 298 K. In the actinic region (λ > 290 nm), an upper limit of 10^–23 cm² molecule^–1 for the absorption cross sections (σ_λ) was reported. Photolysis in the troposphere is therefore expected to be a negligible loss for these fluoropropanols. In addition, absolute rate coefficients for the reaction of OH radicals with CHF₂CF₂CH₂OH (<i>k</i>₁) and CF₃CF₂CH₂OH (<i>k</i>₂) were determined as a function of temperature (<i>T</i> = 263–358 K) by the pulsed laser photolysis/laser induced fluorescence (PLP-LIF) technique. At room temperature, the average values obtained were <i>k</i>₁ = (1.85 ± 0.07) × 10^–13 cm³ molecule^–1 s^–1 and <i>k</i>₂ = (1.19 ± 0.03) × 10^–13 cm³ molecule^–1 s^–1. The observed temperature dependence of <i>k</i>₁(<i>T</i>) and <i>k</i>₂(<i>T</i>) is described by the following expressions: (1.35 ± 0.23) × 10^–12 exp{−(605 ± 54)/<i>T</i>} and (1.36 ± 0.19) × 10^–12 exp{−(730 ± 43)/<i>T</i>} cm³ molecule^–1 s^–1, respectively. Since photolysis of TFPO and PFPO in the actinic region is negligible, the tropospheric lifetime (τ) of these species can be approximated by the lifetime due to the homogeneous reaction with OH radicals. Global values of τ_OH were estimated to be of 3 and 4 months for TFPO and PFPO, respectively. GWPs relative to CO₂ at a time horizon of 500 years were calculated to be 8 and 12 for TFPO and PFPO, respectively. Despite the higher GWP relative to CO₂, these species are not expected to significantly contribute to the greenhouse effect in the next decades since they are short-lived species and will not accumulate in the troposphere even as their emissions grow up

Laboratory Studies of CHF₂CF₂CH₂OH and CF₃CF₂CH₂OH: UV and IR Absorption Cross Sections and OH Rate Coefficients between 263 and 358 K

Fluorinated alcohols, such as 2,2,3,3-tetrafluoropropanol (TFPO, CHF₂CF₂CH₂OH) and 2,2,3,3,3-pentafluoropropanol (PFPO, CF₃CF₂CH₂OH), can be potential replacements of hydrofluorocarbons with large global warming potentials, GWPs. IR absorption cross sections for TFPO and PFPO were determined between 4000 and 500 cm^–1 at 298 K. Integrated absorption cross sections (<i>S</i>_int, base <i>e</i>) in the 4000–600 cm^–1 range are (1.92 ± 0.34) × 10^–16 cm² molecule^–1 cm^–1 and (2.05 ± 0.50) × 10^–16 cm² molecule^–1 cm^–1 for TFPO and PFPO, respectively. Uncertainties are at a 95% confidence level. Ultraviolet absorption spectra were also recorded between 195 and 360 nm at 298 K. In the actinic region (λ > 290 nm), an upper limit of 10^–23 cm² molecule^–1 for the absorption cross sections (σ_λ) was reported. Photolysis in the troposphere is therefore expected to be a negligible loss for these fluoropropanols. In addition, absolute rate coefficients for the reaction of OH radicals with CHF₂CF₂CH₂OH (<i>k</i>₁) and CF₃CF₂CH₂OH (<i>k</i>₂) were determined as a function of temperature (<i>T</i> = 263–358 K) by the pulsed laser photolysis/laser induced fluorescence (PLP-LIF) technique. At room temperature, the average values obtained were <i>k</i>₁ = (1.85 ± 0.07) × 10^–13 cm³ molecule^–1 s^–1 and <i>k</i>₂ = (1.19 ± 0.03) × 10^–13 cm³ molecule^–1 s^–1. The observed temperature dependence of <i>k</i>₁(<i>T</i>) and <i>k</i>₂(<i>T</i>) is described by the following expressions: (1.35 ± 0.23) × 10^–12 exp{−(605 ± 54)/<i>T</i>} and (1.36 ± 0.19) × 10^–12 exp{−(730 ± 43)/<i>T</i>} cm³ molecule^–1 s^–1, respectively. Since photolysis of TFPO and PFPO in the actinic region is negligible, the tropospheric lifetime (τ) of these species can be approximated by the lifetime due to the homogeneous reaction with OH radicals. Global values of τ_OH were estimated to be of 3 and 4 months for TFPO and PFPO, respectively. GWPs relative to CO₂ at a time horizon of 500 years were calculated to be 8 and 12 for TFPO and PFPO, respectively. Despite the higher GWP relative to CO₂, these species are not expected to significantly contribute to the greenhouse effect in the next decades since they are short-lived species and will not accumulate in the troposphere even as their emissions grow up

Laboratory Studies of CHF₂CF₂CH₂OH and CF₃CF₂CH₂OH: UV and IR Absorption Cross Sections and OH Rate Coefficients between 263 and 358 K

Fluorinated alcohols, such as 2,2,3,3-tetrafluoropropanol (TFPO, CHF₂CF₂CH₂OH) and 2,2,3,3,3-pentafluoropropanol (PFPO, CF₃CF₂CH₂OH), can be potential replacements of hydrofluorocarbons with large global warming potentials, GWPs. IR absorption cross sections for TFPO and PFPO were determined between 4000 and 500 cm^–1 at 298 K. Integrated absorption cross sections (<i>S</i>_int, base <i>e</i>) in the 4000–600 cm^–1 range are (1.92 ± 0.34) × 10^–16 cm² molecule^–1 cm^–1 and (2.05 ± 0.50) × 10^–16 cm² molecule^–1 cm^–1 for TFPO and PFPO, respectively. Uncertainties are at a 95% confidence level. Ultraviolet absorption spectra were also recorded between 195 and 360 nm at 298 K. In the actinic region (λ > 290 nm), an upper limit of 10^–23 cm² molecule^–1 for the absorption cross sections (σ_λ) was reported. Photolysis in the troposphere is therefore expected to be a negligible loss for these fluoropropanols. In addition, absolute rate coefficients for the reaction of OH radicals with CHF₂CF₂CH₂OH (<i>k</i>₁) and CF₃CF₂CH₂OH (<i>k</i>₂) were determined as a function of temperature (<i>T</i> = 263–358 K) by the pulsed laser photolysis/laser induced fluorescence (PLP-LIF) technique. At room temperature, the average values obtained were <i>k</i>₁ = (1.85 ± 0.07) × 10^–13 cm³ molecule^–1 s^–1 and <i>k</i>₂ = (1.19 ± 0.03) × 10^–13 cm³ molecule^–1 s^–1. The observed temperature dependence of <i>k</i>₁(<i>T</i>) and <i>k</i>₂(<i>T</i>) is described by the following expressions: (1.35 ± 0.23) × 10^–12 exp{−(605 ± 54)/<i>T</i>} and (1.36 ± 0.19) × 10^–12 exp{−(730 ± 43)/<i>T</i>} cm³ molecule^–1 s^–1, respectively. Since photolysis of TFPO and PFPO in the actinic region is negligible, the tropospheric lifetime (τ) of these species can be approximated by the lifetime due to the homogeneous reaction with OH radicals. Global values of τ_OH were estimated to be of 3 and 4 months for TFPO and PFPO, respectively. GWPs relative to CO₂ at a time horizon of 500 years were calculated to be 8 and 12 for TFPO and PFPO, respectively. Despite the higher GWP relative to CO₂, these species are not expected to significantly contribute to the greenhouse effect in the next decades since they are short-lived species and will not accumulate in the troposphere even as their emissions grow up

Atmospheric Degradation Initiated by OH Radicals of the Potential Foam Expansion Agent, CF₃(CF₂)₂CHCH₂ (HFC-1447fz): Kinetics and Formation of Gaseous Products and Secondary Organic Aerosols

The assessment of the atmospheric impact of the potential foam expansion agent, CF₃(CF₂)₂CHCH₂ (HFC-1447fz), requires the knowledge of its degradation routes, oxidation products, and radiative properties. In this paper, the gas-phase reactivity of HFC-1447fz with OH radicals is presented as a function of temperature, obtaining k_OH(<i>T</i> = 263–358 K) = (7.4 ± 0.4) × 10^–13exp­{(161 ± 16)/<i>T</i>} (cm³·molecule^–1·s^–1) (uncertainties: ±2σ). The formation of gaseous oxidation products and secondary organic aerosols (SOAs) from the OH + HFC-1447fz reaction was investigated in the presence of NO_<i>x</i> at 298 K. CF₃(CF₂)₂CHO was observed at low- and high-NO_<i>x</i> conditions. Evidence of SOA formation (ultrafine particles in the range 10–100 nm) is reported with yields ranging from 0.12 to 1.79%. In addition, the absolute UV (190–368 nm) and IR (500–4000 cm^–1) absorption cross-sections of HFC-1447fz were determined at room temperature. No appreciable absorption in the solar actinic region (λ > 290 nm) was observed, leaving the removal by OH radicals as the main atmospheric loss process for HFC-1447fz. The major contribution of the atmospheric loss of HFC-1447fz is due to OH reaction (84%), followed by ozone (10%) and chlorine atoms (6%). Correction of the instantaneous radiative efficiency (0.36 W m^–2·ppbv^–1) with the relatively short lifetime of HFC-1447fz (ca. 8 days) implies that its global warming potential at a time horizon of 100 year is negligible (0.19) compared to that of HCFC-141b (782) and to that of modern foam-expansion blowing agents (148, 882, and 804 for HFC-152a, HFC-245fa and HFC-365mfc, respectively)

pH-Sensitive Fluorescence Lifetime Molecular Probes Based on Functionalized Tristyrylbenzene

The dependence of the fluorescence on pH for two 1,3,5-tristyrylbenzenes decorated with polyamine (compound <b>1</b>) and poly­(amidoamine) (compound <b>2</b>) chains at the periphery was investigated. The highest fluorescence intensities were observed under acidic conditions because electrostatic repulsions between positively charged molecules reduce the fluorescence quenching. The slopes observed in the fluorescence pH titration curves were associated with deprotonation of the different types of amine groups, which results in quenching by photoinduced electron transfer and aggregation processes. The linear dependence of fluorescence lifetime observed for different pH ranges is a valuable property for applications in the field of fluorescence lifetime sensors and imaging microscopy. The influence of the pH and the peripheral chains on the aggregation processes was also analyzed by absorption and emission spectroscopy, dynamic light scattering measurements, and transmission electron microscopy. For compound <b>1</b>, bands associated with the formation of aggregates were detected along with micrometric aggregates surrounded by fibers with lattice fringes typical of columnar mesophases. For compound <b>2</b>, which contains longer peripheral chains with a higher degree of branching, aggregates with lower internal order were observed. In this case, the peripheral chains hindered aggregation by π-stacking although the amine groups did allow hydrogen bonding