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We use second harmonic generation (SHG) spectroscopy, molecular dynamics simulation, and theoretical modeling to study the response of the neat liquid water-air interface to changes in the potential of an external electrode positioned near the liquid, but out of direct contact. We observe a parabolic dependence of second harmonic intensity on applied potential. Based on standard theory, we associate this dependence with the response of the diffuse layer water molecules to changes in interfacial potential profile. Taking the literature value for this response leads to the unexpected conclusion that the electric fields within the diffuse layer are opposite in sign from those originating from the electrodes. This conclusion implies that the traditional continuum-based models of interfacial screening lack the complexity necessary to properly describe the potential profile of the liquid water-vapor interface. Effects such as overscreening in the topmost interfacial layer and extended correlations in the interfacial hydrogen bonding network may play a role in governing the response of the water interface to external fields.

The triggered self-assembly of surfactants into organized layers at aqueous interfaces is important for creating adaptive nanosystems and understanding selective ion extraction. While these transformations require molecular recognition, the underlying driving forces are modified by the local environment in ways that are not well understood. Herein, we investigate the role of ion binding and ion hydration using cyanosurf, which is composed of the cyanostar macrocycle, and its binding to anions that are either size-matched or mis-matched and either weakly or highly hydrated. We utilize the supra-amphiphile concept where anion binding converts cyanosurf into a charged and amphiphilic complex triggering its self-organization into monolayers at the air-water interface. Initially, cyanosurf forms aggregates at the surface of a pure water solution. When the weakly hydrated and size-matched hexafluorophosphate (PF

We use second harmonic generation (SHG) spectroscopy, molecular dynamics simulation, and theoretical modeling to study the response of the neat liquid water-air interface to changes in the potential of an external electrode positioned above the liquid out of contact. We observe a parabolic dependence of second harmonic intensity on applied potential. This dependence is reminiscent of bulk-phase electric field induced second harmonic (EFISH) but more complicated because it combines the second-order response of the topmost water layer and the potential dependent response of the interfacial electrical double-layer. Based on the literature values for these contributions, we derive a physical interpretation of our measurements that reveals new insight into the response of the neat water interface to external electric fields. Specifically, we find that the net dipolar orientation of water molecules within the double-layer is primarily responsive to the internal fields generated by the excess surface concentrations of OH- and H3O+ that arise to screen the external potential. Notably, this interpretation implies that the orientational response of water dipoles at the interface can actually oppose the direction of the external field, a subtle effect that is not captured by traditional models.

The reactions of 1-chlorocyclopentene with tropospheric oxidants, Cl, OH and O3 are studied to measure the rate coefficients at 298 K and 800 Torr of N2 using the relative rate method with butene, cyclopentene and butane as references. The concentrations of the organics are measured by Gas Chromatograpy technique. The measured average rate coefficient values of kCl, kOH and kO3 (in cm3 molecule−1 s−1) are (3.51 ± 1.26) x 10−10, (5.97 ± 1.08) x 10−11 and (1.50 ± 0.19) x 10−17, respectively. In addition, the rate coefficient for reaction of OH with 1-chlorocyclopentene at 298 K and 30 Torr was also measured using an absolute method of laser photolysis-laser induced fluorescence technique, and the kOH value is found to be (6.01 ± 0.70) x 10−11 cm3 molecule−1 s−1. The stable products formed during the reaction of Cl, OH and O3 initiated oxidation of the 1-chlorocyclopentene in presence of air are characterized by GCMS. The abstraction and addition products are identified among them, the latter are found to be major products. The experimental results are supported by molecular orbital calculations, and abstraction of the allylic hydrogen atoms is predicted to be the major abstraction channel. Calculations predict the preferential addition of chlorine atom to the carbon atom of the unsaturation center not having Cl attached to it. The rate coefficients of 1-chlorocyclopentene are compared with that of cyclopentene and substituted cyclopentene to understand the effect of substituent Cl on the reactivity. The measured rate coefficients have been used to calculate tropospheric lifetime of the compound to be 316, 2 and 26 h for Cl, OH and O3, respectively. Based on these values, the major degradation pathway of 1-chlorocyclopentene is suggested to be its reaction with OH. Atmospheric impact of these molecules is local as tropospheric lifetime (τ)

We use second harmonic generation (SHG) spectroscopy, molecular dynamics simulation, and theoretical modeling to study the response of the neat liquid water-air interface to changes in the potential of an external electrode positioned above the liquid. We observe a parabolic dependence of second harmonic intensity on applied potential. This dependence is reminiscent of bulk-phase electric field induced second harmonic (EFISH) but more complicated because it combines the second-order response of the topmost water layer and the potential dependent response of the interfacial electrical double-layer. Based on the literature values for these contributions, we derive a physical interpretation of our measurements that reveals new insight into the response of the neat water interface to external electric fields. Specifically, we find that the net dipolar orientation of water molecules within the double-layer is primarily responsive to the internal fields generated by the excess surface concentrations of OH- and H3O+ that arise to screen the external potential. Notably, this interpretation implies that the orientational response of water dipoles at the interface can actually oppose the direction of the external field, a subtle effect that is not captured by traditional models.

We use second harmonic generation spectroscopy, molecular dynamics simulation, and theoretical modeling to study the response of the neat liquid water-air interface to changes in the potential of an external electrode positioned above the liquid. We observe a parabolic dependence of second harmonic intensity on applied potential, indicating that water’s net interfacial dipole responds linearly. We also observe a minimum intensity when the potential is tuned to a specific positive value. Interpreting this minimum based on the macroscopic electrostatic potential profile yields misleading physical conclusions because it neglects the internal bias exerted on molecular orientations by the excess surface concentrations of OH- or H3O+. We thus find that water’s net interfacial dipole orientation is primarily responsive to the effects of these ionic species rather than the external electric field.

There is a critical need for receptors that are designed to enhance anion binding selectivity at aqueous interfaces in light of the growing importance of separation technologies for environmental sustainability. Here, we conducted the first study of anion binding selectivity across a series of prevalent inorganic oxoanions and halides that bind to a positively charged guanidinium receptor anchored to an aqueous interface. Vibrational sum frequency generation spectroscopy and infrared reflection absorption spectroscopy studies at the water-air interface reveal that the guanidinium receptor binds to an oxoanion series in the order SO42- > H2PO4- > NO3- > NO2- while harboring very weak interactions with the halides in the order I- > Cl- ≈ Br-. In spite of large dehydration penalties for sulfate and phosphate, the more weakly hydrated guanidinium receptor was selective for these oxoanions in contradiction to predictions made from ion partitioning alone, like the Hofmeister series and Collins's rules. Instead, sulfate binding is likely favored by the suppression of dielectric screening at the interface that consequently boosts Coulombic attractions, and thus helps offset the costs of anion dehydration. Geometric factors also favor the oxoanions. Furthermore, the unique placement of iodide in our halide series ahead of the stronger hydrogen-bond acceptors (Cl-, Br-) suggests that the binding interaction also depends upon single-ion surface partitioning from bulk water to the interface. Knowledge of the anion binding preferences displayed by a guanidinium receptor sheds light on the receptor architectures needed within designer interfaces to control selectivity.

We explore in situ the surface properties of marine algal blooms of diatom monocultures by utilizing surface techniques of Brewster angle microscopy (BAM) imaging, vibrational sum frequency generation spectroscopy (SFG), and infrared reflection absorption spectroscopy (IRRAS). Over the course of the bloom, the marine algae produce surface-active biogenic molecules that temporally partition to the topmost interfacial layers and are selectively probed through surface imaging and spectroscopic measurements. BAM images show morphological structural changes and heterogeneity in the interfacial films with increasing density of surface-active biogenic molecules. Film thickness calculations quantified the average surface thickness over time. The image results reveal an ~5 nm thick surface region in the late stages of the bloom which correlates to typical sea surface nanolayer thicknesses. Our surface-specific SFG spectroscopy results show significant diminishing in the intensity of the dangling OH bond of surface water molecules consistent with organic molecules partitioning and replacing water at the air-seawater interface as the algal bloom progresses. Interestingly, we observe a new broad peak appear between 3500 cm-1 to 3600 cm-1 in the late stages of the bloom that is attributed to weak hydrogen bonding interactions of water to the surface-active biogenic matter. IRRAS confirms the presence of organic molecules at the surface as we observe increasing intensity of vibrational alkyl modes and the appearance of a proteinaceous amide band. Our work shows the often overlooked but vast potential of tracking changes in the interfacial regime of small-scale laboratory marine algal blooms. By coupling surface imaging and vibrational spectroscopies to complex, time-evolving, marine-relevant systems, we provide additional insight into unraveling the temporal complexity of sea spray aerosol compositions.

Trifluoroacetic acid (TFA) is released in the atmosphere through its use in the chemical industry and as degradation product of chlorofluorocarbon (CFC) alternatives like hydrofluorocarbons and hydrochlorofluorocarbons. In the present study, we have investigated the OH formation dynamics in the photodissociation of TFA at 193 nm by Laser Photolysis-Laser Induced Fluorescence (LP-LIF) method, as well as stable product formation by GC MS and FTIR. It was found that, ∼26% of the available energy is partitioned into the relative translation of the photoproducts (f(T) = 0.26), which could be explained by presence of an exit barrier of ∼13 kcal/mol in OH formation channel. This result is very similar to OH formation from acetic acid (AA) and difluoroacetic acid (DFA), indicating fluorination at the side chain of aliphatic carboxylic acids does not significantly change the mechanism of C OH bond scission. Our experimental results tallied with the theoretical studies, which suggested that the major OH formation channel in acetic acid and fluoroacetic acid is direct dissociation from the optically excited S1 state through an exit barrier, with some competition from the T1 state. However, quantum yield of OH formation from TFA (0.4) was found to be much smaller than AA (0.8), which is probably caused by higher reaction barrier in T1 state of TFA, compared to AA. CHF3, C2F4, C2F6, CO2, CO, CF3CFO, CF2O and hexafluoropropylene oxide (HFPO) were detected as the stable products of the photolysis of TFA. The theoretically optimized ground state dissociation channels showed significant difference between TFA and AA.

Introduction: Benign breast lesions create a heterogeneous group of pathologies arising from the mammary epithelium or other mammary tissues. Most lesions diagnosed in symptomatic women are benign. Although, the most reliable method for diagnosis of a breast lesion is histological evaluation, the initial investigation method recommended in young females is Sono-mammogram due to its precision in diagnosis in dense fibro-glandular tissue. However, with better imaging proficiency there is also considerable risk of detecting false positive benign lesions. In present study we have assessed the prevalence of various solid benign lesions on high resolution ultrasound along with their utrasonographic features. Materials & Methods- This retrospective descriptive cross sectional study was conducted on 478 women (age range 22-81 years) with breast lumps. The ultrasound examination was performed with AI Xplorer Supersonic Ultrasound machine, using a range of 2-18 MHz linear array transducers. The lesions were classified using American College of Radiology- Breast Imaging-Reporting and Data System (ACR-BI-RADS). BIRADS 2, 3 and biopsy confirmed 4 lesions were included and their imaging features were studied. Results- A total of 478 women with 790 breasts were analysed. Among these, 112 lesions were diagnosed and confirmed as benign. Fibroadenoma was the most common benign lesion followed by Intramammary lymph node. Other entities included Phyllodes, lipoma, intracystic or intraductal papilloma, Lipnecrosis, Fibroadenosis, PASH, Hamartoma, Neurofibroma and Granulomatous. Conclusion- The benign breast lesions form an extremely heterogeneous group of breast diseases. Some lesions are easily diagnosed due to their characteristic appearance; other lesions present with varying and overlapping imaging features during different stages of their evolution. However, USG is very helpful in lesion characterization & thus guiding further management.

The rate coefficient for the gas phase reaction of the OH radical with 1,2-propylene oxide (PPO) has been measured at 298 K using a relative rate method, employing Gas Chromatography (GC) technique, using ethane and 1,2-dichloroethane as reference compounds. Temperature dependence of the above reaction is also studied using an absolute rate method, employing Laser Photolysis-Laser Induced Fluorescence (LP-LIF) technique, over a range of 261–335 K. The measured bimolecular rate coefficients were fitted into the Arrhenius plot, which yielded a straight line roughly parallel to the x-axis and implies no or very weak temperature dependence. Within the experimental error limits, rate coefficients obtained at various temperatures, are found to vary within a narrow range from (4.65 ± 0.24) × 10−13 to (4.80 ± 0.24) × 10−13 cm3 molecule−1 s−1. Room temperature rate coefficient of the reaction of PPO with the OH radical was found to be (4.65 ± 0.24) × 10−13 cm3 molecule−1 s−1, using LP-LIF technique. These results have been discussed with available literature to unveil the probable mechanism. An average tropospheric lifetime of PPO has been estimated to be about two weeks for degradation by the OH radical. In addition, atmospheric parameters such as Radiative Efficiency (RE) and Global Warming Potential (GWP) for PPO are determined. Stable products formed are characterized using GC-MS and FT-IR techniques. Theoretical calculations are performed to understand the energetics and mechanism of H atom abstraction by OH, and also to complement the experimental observations.

The photodissociation dynamics of benzoyl chloride at 235 nm has been investigated and compared with that of 2-furoyl chloride. Atomic Cl and molecular HCl channels have been detected in benzoyl chloride by employing resonance-enhanced multiphoton ionization technique and time-of-flight mass spectrometry. Both the Cl fragments, Cl((2)PJ=3/2, relative quantum yield 0.70 ± 0.15) and Cl*((2)PJ=1/2), show isotropic angular distribution and bimodal translational energy distributions. The predominant high kinetic energy channel contributes 72% to the C-Cl bond scission and arises from the S1 state having nπ* character of benzoyl chloride. However, the low-energy Cl and HCl channels originate from the ground electronic state. The most plausible mechanism of HCl formation is proposed based on molecular orbital calculations. In contrast to benzoyl chloride, the HCl channel is not observed in 2-furoyl chloride on excitation at 235 nm, and this is attributed to an energy constraint.

The photodissociation dynamics of phosphorus trichloride (PCl(3)) has been studied in a supersonic beam by resonance enhanced multiphoton ionization (REMPI), using time-of-flight (TOF) mass spectrometry. The study is focused on the nascent state of the primary chlorine atom, formed on excitation of the (n, sigma*) transition of the molecule around 235 nm. Dissociation of PCl(3) and the REMPI detection of chlorine atoms are performed, using the same laser around 235 nm. The photofragments, namely, Cl((2)P(3/2)) and Cl*((2)P(1/2)), are probed, using the 2+1 REMPI scheme in the 234-236 nm region. We have determined the photofragment speed distribution, the recoil anisotropy parameter beta, and the spin-orbit branching ratio for chlorine atom elimination channels. Polarization-dependent and state-specific TOF profiles are converted into kinetic energy distributions, using a least-squares fitting method, taking into account the fragment anisotropies. The anisotropy parameters for Cl and Cl* are characterized by values of 0.0 +/- 0.05 and 0.20 +/- 0.05, respectively. Two components, namely, the fast and the slow, are observed in the speed distribution (P(v)) of Cl and Cl* atoms, formed from different potential energy surfaces. The average translational energies for the Cl and Cl* channels for the fast component are 29.7 and 30.6 kcal/mol, respectively. Similarly, for the slow component, the average translational energies for the Cl and Cl* channels are 9.5 and 9.1 kcal/mol, respectively. The energy partitioning into the translational modes is interpreted with the help of an impulsive model, for the fast component, and a statistical model, for the slow component. Apart from the chlorine atom elimination channel, molecular chlorine (Cl(2)) elimination is also observed in the photodissociation of PCl(3). The observation of the molecular chlorine in the dissociation process and the bimodal translational energy distribution of the chlorine atom clearly indicate the existence of a crossover mechanism from the initially prepared state to the ground state.

The photodissociation dynamics of 1,2-cyclohexanedione (CHD), which exists in enolic form in gas phase, is studied using pulsed laser photolysis (LP)-laser induced fluorescence (LIF) "pump-and-probe" technique at room temperature. The nascent state distribution of the OH radical, formed after initial photoexcitation of the molecule to it is (π, π*) and Rydberg states, is determined. The initial (π, π*) and Rydberg states are prepared by excitation with the fourth harmonic output of Nd:YAG (266 nm)/KrF (248 nm) and ArF (193 nm) lasers, respectively. The ro-vibrational distribution of the nascent OH photofragment is measured in collision-free conditions using LIF. The OH fragments are formed in the vibrationally cold state at all the above wavelengths of excitation but differ in rotational state distributions. At 266 nm photolysis, the rotational population of OH shows a curvature in Boltzmann plot, which is fairly described by two types of Boltzmann-like distributions characterized by rotational temperatures of 3100 ± 100 and 900 ± 80 K. However, at 248 nm photolysis, the rotational distribution is described by a single rotational temperature of 950 ± 80 K. The spin-orbit and Λ-doublets ratios of OH fragments formed in the dissociation process are also measured. The average translational energy in the center-of-mass coordinate, partitioned into the photofragment pairs of the OH formation channels, is determined to be 12.5 ± 3.0, 12.7 ± 3.0, and 12.0 ± 3.0 kcal/mol at 266, 248, and 193 nm excitation, respectively. The energy partitioning into various degrees of freedom of products is interpreted with the help of different models, namely, statistical, impulsive, and hybrid models. To understand the nature of the dissociative potential energy surface involved in the OH formation channel, detailed ab initio calculations are performed using configuration interaction-singles (CIS) method. It is proposed that at 266 nm photolysis, the OH fragment is formed from two different excited state structures, one with a strong H bonding, similar to that in the ground state, and another without effective H bonding, whereas, at 248 nm photodissociation, it seems that the OH formation occurs mainly from the excited state, which lacks effective H-bonding. At 193 nm excitation, the initially prepared population in the Rydberg state crosses over to a nearby σ* repulsive state along the C-O bond, from where the dissociation takes place. The exit barrier for the OH dissociation channel is estimated to be 14 kcal/mol. The existence of dynamical constraint due to strong hydrogen bond in the ground state is effectively present in the dissociation process at 266 and somewhat deficient at 248 nm photolysis.

The photodissociation dynamics of halogen-substituted thiophenes, namely, 2-chlorothiophene and 2-bromo-5-chlorothiophene, has been studied in a supersonic molecular beam around 235 nm, using resonance enhanced multiphoton ionization (REMPI) time-of-flight (TOF) technique, by detecting the nascent state of the primary halogen atoms. A single laser has been used for excitation of halothiophenes, as well as for the REMPI detection of photoproducts, namely, chlorine and bromine atoms, in their spin-orbit states X((2)P(3/2)) and X*((2)P(1/2)). We have determined the translational energy distribution, the recoil anisotropy parameter, β, and the spin-orbit branching ratio, for chlorine and bromine atom elimination channels. State-specific TOF profiles are converted into kinetic energy distributions, using a least-squares fitting method, taking into account the fragment anisotropies, β(ι). The TOF profiles for Cl, Cl*, Br, and Br* are found to be independent of laser polarization; i.e., the β is well characterized by a value of ~0.0, within the experimental uncertainties. For 2-chlorothiophene, we have observed two components for the Cl and only one component for the Cl* atom elimination channel in the translational energy distributions. The average translational energies for the fast and the slow components of the Cl channel are 3.0 ± 1.0 and 1.0 ± 0.5 kcal/mol, respectively. For Cl*, the average translational energy is 3.5 ± 1.0 kcal/mol. For 2-bromo-5-chlorothiophene, we have observed only one component for Cl, Cl*, Br, and Br* in the translational energy distributions. The average translational energies for the Cl and Cl* channels are 3.5 ± 1.0 and 5.0 ± 1.0 kcal/mol, respectively, whereas the average translational energies for the Br and Br* channels are 2.0 ± 1.0 and 3.5 ± 1.0 kcal/mol, respectively. The energy partitioning into the translational modes is interpreted with the help of various models, such as impulsive and statistical models. The ΔH(f)(298) value for 2-chlorothiophene has been estimated theoretically to be 23.5 kcal/mol.

The photodissociation dynamics of fumaryl chloride (ClCO-CH═CH-COCl) has been studied in a supersonic molecular beam around 235 nm using resonance enhanced multiphoton ionization (REMPI) time-of-flight (TOF) technique by detecting the nascent state of the primary chlorine atom. A single laser has been used for excitation of fumaryl chloride and the REMPI detection of chlorine atoms in their spin-orbit states, Cl ((2)P(3/2)) and Cl* ((2)P(1/2)). We have determined the translational energy distribution, the recoil anisotropy parameter, β, and the spin-orbit branching ratio for chlorine atom elimination channels. To obtain these, measured polarization-dependent and state-specific TOF profiles are converted into kinetic energy distributions, using a least-squares fitting method, taking into account the fragment recoil anisotropies, β(i). The TOF profiles for both Cl and Cl* are found to be independent of laser polarization; i.e., β is well characterized by a value of 0.0, within the experimental uncertainties. Two components, namely, the fast and the slow, are observed in the translational energy distribution, P(E(T)), of Cl and Cl* atoms, and assigned to be formed from different potential energy surfaces. The average translational energies for the fast components of the Cl and Cl* channels are 14.9 ± 1.6 and 16.8 ± 1.6 kcal/mol, respectively. Similarly, for the slow components, the average translational energies of the Cl and Cl* channels are 3.4 ± 0.8 and 3.1 ± 0.8 kcal/mol, respectively. The energy partitioning into the translational modes is interpreted with the help of various models, such as impulsive and statistical models. Apart from the chlorine atom elimination channel, molecular hydrogen chloride (HCl) elimination is also observed in the photodissociation process. The HCl product has been detected, using a REMPI scheme in the region of 236-237 nm. The observation of the molecular HCl in the dissociation process highlights the importance of the relaxation process, in which the initially excited parent molecule relaxes to the ground state from where the molecular (HCl) elimination takes place.

Cyclohexanone oxime (CHO) and cyclopentanone oxime (CPO) in the vapor phase undergo N-OH bond scission upon excitation at 193 nm to produce OH, which was detected state selectively employing laser-induced fluorescence. The measured energy distribution between fragments for both oximes suggests that in CHO the OH produced is mostly vibrationally cold, with moderate rotational excitation, whereas in CPO the OH fragment is also formed in v'' = 1 (~2%). The rotational population of OH (v'' = 0, J'') from CHO is characterized by a rotational temperature of 1440 ± 80 K, whereas the rotational populations of OH (v'' = 0, J'') and OH (v'' = 1, J'') from CPO are characterized by temperatures of 1360 ± 90 K and 930 ± 170 K, respectively. A high fraction of the available energy is partitioned to the relative translation of the fragments with f(T) values of 0.25 and 0.22 for CHO and CPO, respectively. In the case of CHO, the Λ-doublet states of the nascent OH radical are populated almost equally in lower rotational quantum levels N'', with a preference for Π(+) (A') states for higher N''. However, there is no preference for either of the two spin orbit states Π(3/2) and Π(1/2) of OH. The nascent OH product in CPO is equally distributed in both Λ-doublet states of Π(+) (A') and Π(-) (A'') for all N'', but has a preference for the Π(3/2) spin orbit state. Experimental work in combination with theoretical calculations suggests that both CHO and CPO molecules at 193 nm are excited to the S(2) state, which undergoes nonradiative relaxation to the T(2) state. Subsequently, molecules undergo the N-OH bond dissociation from the T(2) state with an exit barrier to produce OH (v'', J'').