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A continuous plug flow reactor supported by a dielectric barrier discharge (DBD) is used to study the conversion of methane, carbon dioxide, and oxygen at different compositions. The three studied gases were diluted with helium to 3 % with an overall flow rate of 200 sccm. The 13.56 MHz plasma was ignited at atmospheric pressure. The product stream and the inlet flow were analyzed by a FTIR spectrometer equipped with a White-cell and by a quadrupole mass spectrometer. The DBD reactor generates hydrogen, carbon monoxide, ethane, ethene, acetylene, formaldehyde, and methanol. Additional oxygen in the feed has positive effects on the yield of methanol, formaldehyde and carbon monoxide and reduces the total consumed energy. The hydrogen yield reaches its maximum at medium amounts of oxygen in the inlet flow. The conversion of methane increases to a limiting value of about 35 %. Methane rich feeds increase the yield of hydrogen, ethane and methanol. On the other hand, additional oxygen has a negative influence on the produced amount of C2 hydrocarbons. The conversion of methane and carbon dioxide as well as the yield of synthesis gas components and C2 hydrocarbons increases by changing the plasma power to higher values.

The conversion of biogas like mixtures of methane and carbon dioxide was studied in a plug flow reactor with a dielectric barrier discharge. A 13.56 MHz power supply generated the atmospheric plasma discharge. Studied concentration of methane ranged from 0 to 100%, with missing part filled up with carbon dioxide. This mixture was diluted with helium to 2.5% with small part of the product stream monitored online at a total pressure of 100 mbar by a Fourier transform infrared spectrometer supported by a White-cell and a quadrupole mass spectrometer. The reactor was driven at different flow rates. This DBD reactor produces all three hydrocarbons, with ethane being the major compound. The concentration of ethane increases when the power in the plasma region increases from 30 to 65 W. This product concentration also grows up, if the fraction of methane in the inlet flow is increased. The highest amount of ethane (5.4%) is produced, when the gas stream consist of 2.5% Methane and 97.5% helium at a flow rate of 200 sccm.

Modified hydroxyethyl starch is photo-crosslinked in the presence of a green fluorescent protein (GFP) (mTagGFP) to obtain loaded hydrogels as model for a drug-delivery system. An important factor for the protein release is the crosslinking density since a dense network should lead to hindered diffusion. To obtain information on the rotational and translational diffusion of GFP in the hydrogel, mTagGFP is analyzed by fluorescence anisotropy and fluorescence recovery after photo-bleaching experiments using two-photon excitation. The mTagGFP shows a viscosity-retarded rotational and strongly hindered translational diffusion, depending on the polymer concentration. A comparison of anisotropy studies with mTagGFP-loaded microparticles and hydrogel disks allows the polymer concentration to be determined for the microparticles, which has been previously unknown.

The influence of water on the plasma assisted conversion of methane and carbon dioxide in a dielectric barrier discharge (DBD) plug flow reactor was studied. The plasma at atmospheric pressure was ignited by a power supply at a frequency of 13.56 MHz. Product formation was studied at a power range between 35 and 70 W. The concentrations of the three gases were altered and diluted with helium to 3 %. FTIR spectroscopy and mass spectroscopy were applied to analyze the inlet and the product streams. The main product of this process are hydrogen, carbon monoxide and ethane. Ethene, ethine, methanol and formaldehyde are generated beside the main products in this DBD in lower concentrations. The conversion of methane, the ratio of the synthesis gas components (n(H2):n(CO)), and the yield of oxygenated hydrocarbons and hydrogen increases by adding water. The total consumed energy reaches lower values for small amounts of water. Additional water does not influence the generated amount of C2 hydrocarbons and of CO, but decreases the carbon dioxide conversion.

The catalytic conversion of methane and carbon dioxide was studied in a fluidized bed reactor supported by a 13.56 Hz driven coaxial DBD-reactor. Palladium or cupper catalyst which are covered on Al2O3 particles were used. The goal was to test whether biogas can be used for the production of synthesis gas. The influences of discharge power, catalysts and temperature of the catalyst bed on the product yield were studied. The starting material and product stream was analyzed by quadrupole mass spectrometry and infrared spectroscopy. H2/CO ratios can be adjusted in a range between 0.65 (without a catalyst) and 1.75 (using a copper catalyst). The process is highly selective for hydrogen production (up to 83%, using a Palladium catalyst). A copper catalyst increases the H2/CO ratio can from 1.04 to 1.16 and the palladium catalyst from 1.11 to 1.43 by heating the catalyst to a temperature of 250°C.

Encapsulation of molecules in phospholipid vesicles provides unique opportunities to study chemical reactions in small volumes as well as the behavior of individual proteins, enzymes, and ribozymes in a confined region without requiring a tether to immobilize the molecule to a surface. These experiments generally depend on generating a predictable loading of vesicles with small numbers of target molecules and thus raise a significant measurement challenge, namely, to quantify molecular occupancy of vesicles at the single-molecule level. In this work, we describe an imaging experiment to measure the time-dependent fluorescence from individual dye molecules encapsulated in ~130 nm vesicles that are adhered to a glass surface. For determining a fit of the molecular occupancy data to a Poisson model, it is critical to count empty vesicles in the population since these dominate the sample when the mean occupancy is small, λ ≤ ~1. Counting empty vesicles was accomplished by subsequently labeling all the vesicles with a lipophilic dye and reimaging the sample. By counting both the empty vesicles and those containing fluors, and quantifying the number of fluors present, we demonstrate a self-consistent Poisson distribution of molecular occupancy for well-solvated molecules, as well as anomalies due to aggregation of dye, which can arise even at very low solution concentrations. By observation of many vesicles in parallel in an image, this approach provides quantitative information about the distribution of molecular occupancy in a population of vesicles.

The competition between multiphoton ionization and fragmentation in the diatomic molecule hydrogen chloride is reviewed. Emphasis is laid on recent experimental results employing chemical imaging methods in order to obtain kinetic energy distributions and angular distributions of photoproducts. The energy range considered is 15 to 20 eV, equivalent to the absorption of three or four photons in the ultraviolet wavelength range. The role of Rydberg states as resonantly excited intermediate states in the ionization/fragmentation processes is assessed. Mixing among Σ1+ states gives rise to peculiarly shaped double minimum potential energy curves which allow for the production of hydrogen and chlorine atomic and ionic fragments via several competing pathways, in addition to the production of molecular HCl+ ions. States with different electronic properties show a qualitatively different behaviour from Σ+ states. Accidental resonances between states of differing orbital angular momentum or multiplicity serve to override these differences and cause subtle as well as significant deviations from the unperturbed behaviour.

We report a general theory of the two-photon excited fluorescence (TPEF) of rotating molecules under the condition of anisotropic depolarisation. The obtained expressions for the TPEF intensity are based upon the spherical tensor approach and valid for any symmetric, or asymmetric top molecule and for any photon polarisation. The expressions are written in terms of the molecular parameters M K (R, R′, t) which have clear tensor notation and contain all molecular information that can be extracted from the TPEF experiments. Two important extreme cases are discussed. If the molecular rotation period is much larger than the excited state lifetime, the obtained expressions describe the TPEF in non-rotating molecules under the condition of isotropic relaxation. The time-independent part of these expressions is in agreement with the earlier results of McClain [J. Chem. Phys., 58, 324 (1973)]. The relationship between McClain's molecular parameters and the parameters M K (R, R′, 0) is presented and analysed. If t...

The hybrid plasma-catalytic system was tested for the mixture of methane and CO2 conversion at the pressure of 1.2 bar with the use of a dielectric barrier discharge (DBD) reactor powered at the frequency of 5.7–6 kHz. Three kinds of catalytic packing were examined: alumina ceramic carrier (Al2O3) and two catalysts, i.e. Ag/Al2O3 and Pd/Al2O3. The effects of temperature (120–290 °C), [CO2]:[CH4] molar ratio in the inlet gas mixtures (CH4 + CO2 + Ar), gas flow rate, and specific energy on the conversion were studied. Hydrogen, carbon oxide, hydrocarbons (ethane, ethylene + acetylene fraction, propane, propylene, n-butane, and i-butane), and alcohols (methanol and ethanol) were identified in the outlet gas. Among the organic gaseous products, ethane was dominant over the entire parameter range under examination. Non-volatile products (carbon, macromolecular substances) formed a visible deposit on the quartz dielectric barrier and metal electrode surfaces. With the Pd/Al2O3 catalyst, the overall methane conversion was 30–50% and the methane conversion to C2–C4 hydrocarbons reached 22%.

The use of two-color two-photon (2c2p) excitation easily extends the wavelength range of Ti:sapphire lasers to the UV, widening the scope of its applications especially in biological sciences. We report observation of 2c2p excitation fluorescence of p-terphenyl (PTP), 2-methyl-5-t-butyl-p-quaterphenyl (DMQ) and tryptophan upon excitation with 400 and 800 nm wavelengths using the second harmonic and fundamental wavelength of a mode-locked Ti:sapphire femtosecond laser. This excitation is energetically equivalent to a one-photon excitation wavelength at 266 nm. The fluorescence signal is observed only when both wavelengths are spatially and temporally overlapping. Adjustment of the relative delay of the two laser pulses renders a cross correlation curve which is in good agreement with the pulse width of our laser. The fluorescence signal is linearly dependent on the intensity of each of the two colors but quadratically on the total incident illumination power of both colors. In fluorescence microscopy, the use of a combination of intense IR and low-intensity blue light as a substitute for UV light for excitation can have numerous advantages. Additionally, the effect of differently polarized excitation photons relative to each other is demonstrated. This offers information about different transition symmetries and yields deeper insight into the two-photon excitation process.

In the last decade, the two-photon fluorescence laser-scanning microscopy (TPLSM) has become an indispensable tool for the bioscientific and biomedical research. TPLSM techniques as well as their applications are currently experiencing a dramatic evolution and represent the focus of many biophysical research projects. In this work, we compare in detail two steady-state TPLSM techniques, i.e. single-beam scanning microscopy combined with point-detection (SB-PMT) and multi-beam scanning microscopy combined with synchronous detection (MB-CCD), as far as their technical characteristics relevant for the bioscientific research are concerned, i.e. optical performance and imaging speed. We demonstrate that the SB-PMT technique is more adequate for deep-tissue imaging (few 100??m depth) than the MB-CCD technique, whereas only the MB-CCD technique enables high-speed imaging for characterizing the dynamics of fast biological phenomena. Novel applications of these techniques are additionally discussed. Moreover, we employ a time-resolved TPLSM technique, i.e. biexponential fluorescence lifetime imaging based on the cellular fluorescence of the nicotinamide pyridine dinucleotides NADH and NADPH, which allows us to probe for the first time the redox cellular metabolism of MIN6 cells (mutated insulin producing pancreatic ?-cells) as well as to show the potential of this method for the specific and dynamic investigation of NADH- and NADPH-dependent cellular processes.

The characterisation of a discharge requires the knowledge about few parameters. The most important are the electron density, the debye-length λd and the voltage/current characteristic. Normally the electron density is obtained using a Langmuir Probe. This method delivers reliable results if the influence on the electric field can be neglected. In the analysis of microdischarges, this assumption is not fulfilled. J. Park et al. (J. Appl. Phys.2001, 89, 15), developed a model which allows to calculate the electron density using the plasma current, the area of the discharge and the electric field strength. The debye-length can be estimated using the dimensions of the dark space of the discharge. With this information it is possible to calculate the electron temperature. To measure the dimension of the dark space, it is crucial to take a close look at the discharge. We used an ocular of a microscope (40× magnification) to project an image of one electrode gap onto the sensor of an ICCD-Camera. The electrical parameters were obtained using an ENI V/I-Probe®. The experiments were conducted in helium and argon at atmospheric pressure. In order to cover the whole glow-discharge regime, the applied power was raised in steps of 1 W from the point of ignition to the glow-to-arc transition. Electron densities and temperatures as well as the debye-length could be obtained.

We present a detailed study of two-color two-photon excited fluorescence in indole dissolved in propylene glycol. Femtosecond excitation pulses at eff ective wavelengths from 268 to 293.33 nm were used to populate the two lowest indole excited states 1 La and 1 Lb and polarized fluorescence was then detected. All seven molecular parameters and the two-photon polarization ratio Ω containing information on two-photon absorption dynamics, molecular lifetime τf , and rotation correlation time τrot have been determined from experiment and analyzed as a function of the excitation wavelength. The analysis of the experimental data has shown that 1 Lb– 1 La inversion occurred under the conditions of our experiment. The two-photon absorption predominantly populated the 1 La state at all excitation wavelengths but in the 287–289 nm area which contained an absorption hump of the 1 Lb state 0-0 origin. The components of the two-photon excitation tensor S were analyzed giving important information on the principal tensor axes and absorption symmetry. The results obtained are in a good agreement with the results reported by other groups. The lifetime τf and the rotation correlation time τrot showed no explicit dependence on the eff ective excitation wavelength. Their calculated weighted average values were found to be τf = 3.83 ± 0.14 ns and τrot = 0.74 ± 0.06 ns. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4905140]

Micro-structured electrode (MSE) arrays consist of an interlocked, comb like, capacitive electrode system with gap widths in the µm-range. The usage of the Paschen similarity law (pd = const.) enabled us to generate large area uniform glow discharges up to atmospheric pressure with our arrays. In order to ignite glow discharges at atmospheric pressure this approach is established next to using dielectric barrier arrays and plasma jets. Because of the industrial, scientific and medical (ISM) limitation of available radio frequencies the usual frequency for experiments is 13.56 MHz. With a variable radio frequency generator, it is possible to extend the applicability of the MSE arrays in order to gain more information about the frequency dependent breakdown mechanisms and to confirm the underlying theory. The electric parameters of the non-thermal plasma system are characterized by a special probe with an upper frequency detection limit of 60 MHz.

Summary: Micro-structured electrode (MSE) arrays allow large area uniform glow discharges to be generated over a wide pressure range up to atmospheric pressure. Electrode widths, thicknesses and distances in the μm-range are realized by means of modern micro machining and galvanic techniques. These electrode dimensions are small enough to generate sufficiently high electric field strengths to ignite gas discharges by applying only moderate radio frequency (RF, 13.56 MHz) voltages (80 V to 390 V in Ne, He, Ar, N2 and air). The non-thermal plasma system can be characterized by a special probe measuring the electric parameters. MSE driven plasmas demonstrate different behavior from conventional RF or DC discharge plasmas. Due to the very small electrode gap width, d, the behavior of the charged particles in the RF field of our system could be described with the DC Townsend breakdown theory. Partially, dependent on the pressure range and type of gas, the breakdown mechanism was dominated by field electron emission or by a high frequency regime. The voltage-current characteristic and electron density of the MSE plasma in He at atmospheric pressure were characteristic for a glow discharge. Using MSE arrays as plasma sources, several applications have been developed and successfully tested including atmospheric pressure plasma chemistry (decomposition of waste gases like CF4 and NO) and the sterilization of food packaging materials at atmospheric pressure. Voltage-current characteristic of a 100 kPa He RF glow discharge generated with an MSE array (d = 70 μm).

The photodissociation of Cl 2 O has been investigated for adjacent regions in the first and the second absorption bands, respectively, at dissociation wavelengths of 5.3 and 6.0 eV. Chlorine and oxygen atoms were state;electively detected by resonance-enhanced multiphoton ionization. Chlorine fragment kinetic energy and spatial distributions were determined from time-of-flight profile analysis. At 5.3 eV, kinetic energy distributions are broad and bimodal and differ significantly for the two spin-orbit states Cl*( 2 P 1 / 2 ) and Cl( 2 P 3 / 2 ). The decay is characterized by a positive anisotropy parameter of 0.7 ′ 0.2. Excitation proceeds via the transitions 10a 1 ← 7b 2 and 10a 1 ← 9a 1 . The data are in agreement with generating CIO(X) + Cl*( 2 P 1 / 2 ) as primary fragments. At 6.0 eV. kinetic energy distributions are narrow and structureless and are similar for the two spin-orbit states Cl*(2P 1 / 2 ) and Cl( 2 P 3 / 2 ). The decay is characterized by a small positive anisotropy parameter of 0.2 ′ 0.2. The main dissociation channel is the three-body decay into 2Cl + O. The decay mechanism is of an asynchronous concerted type. The data suggest the primary production of ClO(A) + Cl( 2 P J ). Excitation proceeds mainly via the transition 8b 2 ← 7b 2 . The results show the need for refined theoretical calculations.

We present the results of experimental and theoretical studies of the speed-dependent spin–orbit state distributions of chlorine photofragments produced in the photodissociation of thiophosgene (CSCl 2 ) at 235 nm. Three-dimensional imaging has been employed for observing chlorine photofragments in their ground (Cl) and excited (Cl * ) spin–orbit states. The kinetic energy distributions for Cl and Cl * fragments reflect excitation of several electronic states of the partner fragment CSCl. The spin–orbit branching ratio of P (Cl * )/[ P (Cl) + P (Cl * )] was found to depend on the kinetic recoil energy increasing from 0.1 for low kinetic energy to 0.8 for high kinetic energy. The theoretical interpretation is based on the computation of the CSCl 2 potential energy surfaces (PES) along the C–Cl bond. Two completely different methods of determination of the PES were applied for small and for large values of the C–Cl bond separation R . In case of small and intermediate R values time-dependent density-functional theory has been used. In case of large R values we used an asymptotic method of computation of the PES, which is a generalisation of the Heitler–London approach for many-electron systems. Basis molecular wavefunctions with definite values of the total spin S and the spatial and spin reflection symmetry σ v with respect to reflection of the total electronic wavefunction in the molecular plane were used. The developed theoretical approach was used for the assignment of the molecular states involved in the photodissociation and for the qualitative explanation of the non-statistical population of the spin–orbit states of the chlorine photofragments as function of the kinetic energy. The spin–orbit branching ratio of P (Cl * )/[ P (Cl) + P (Cl * )] predicted by the theory strongly depends on the quantum state of the CSCl fragment. It is large in case of the CSCl(X) + Cl and CSCl(A) + Cl channels and small in case of the CSCl(B) + Cl channel which explains the experimental results.

We report the first observation of ion recoil induced by the ionization process for a molecule. The applicability of the method has been demonstrated by determining the b2 and b4 anisotropy parameters of the angular distributions of NO þ ions in the resonanceenhanced two-photon ionization of NO(X 2 P1=2, v ¼ 0; J ) via the A 2 R þ (v � ¼ 0, N � ) state at 226 nm. An energy resolution in the range of 10 leV is demonstrated. The method might prove to be particularly useful for studying complex ionization-fragmentation processes as they occur for example for superexcited molecules. 2004 Elsevier B.V. All rights reserved.

Micro-structured electrode (MSE) arrays allow to generate large-area uniform glow discharges over a wide pressure range up to atmospheric pressure. The electrode dimensions in the μm-range realized by means of modern micro-machining and galvanic techniques are small enough to generate sufficiently high electric field strengths to ignite gas discharges applying only moderate radio frequency (RF, 13.56 MHz) voltages (80–390 V in Ne, He, Ar and N 2 ). The non-thermal plasma system is characterized by a special probe measuring the electric parameters. The MSE-driven plasmas show a different behavior from conventional discharge plasmas depending on the pressure and the type of gas. With the MSE arrays as plasma sources, several applications were developed and successfully tested: Plasma chemistry (decomposition of waste gases like CF 4 ) and thin film deposition (e.g. SiO 2 layers on various substrates). A new atmospheric pressure application realized in our lab is the sterilization of food packaging materials.

The photodissociation of disulfur dichloride (S2Cl2) at 235 nm has been studied by three-dimensional (3D) imaging of the chlorine product recoil in its ground state 2P3/2[Cl] and excited spin–orbit state 2P1/2[Cl*] employing the resonance enhanced multiphoton ionization and time-of-flight techniques. The photodissociation proceeds mainly along the three channels forming S2+2Cl (1), S2Cl+Cl (2), and 2 SCl (3) photoproducts where slow and fast Cl fragments are released in (1) and (2), respectively. The relative yield of channel (1) with respect to channel (2) was determined to be 1.2:1.0. The yield of Cl*, φ(Cl*)=P(Cl*)/[P(Cl)+P(Cl*)], was found to be 0.35. The obtained state-specific velocity distributions of Cl and Cl* are mainly different in the high energy range: For Cl* the two dissociation channels are almost equally present, whereas in the case of ground state Cl the contribution of dissociation channel (2) is of minor importance. The dependence of the anisotropy parameter β on the fragment recoil ve...

The state-resolved and isotope-specific detection of nascent ClO generated from the photodissociation of Cl2O parent molecules is performed by observing single-color (2+1) resonance enhanced multiphoton ionization (REMPI) spectra following excitation in the wavelength range from 336 to 344 nm; additionally state-resolved detection of nascent ClO is performed by observing single-color two photon laser-induced fluorescence. The REMPI spectrum is assigned to the ClO(C 2Σ−,v′=0←X 2ΠΩ,v=0) transition. The population of rotational states up to J=130 is evidence of large rotational excitation induced by a strong dependence of the excited potential energy surface (PES) on the Jacobi angle γ. Formation of the 2Π3/2 spin-orbit state is preferred: P(2Π1/2):P(2Π3/2)=0.30±0.05 suggesting significant radiationless transfer from the excited PES to closely lying neighboring states. The anisotropy parameter for the transition is determined to be β=0.35 independent of the ClO quantum state. The principal excited electronic...

The photodissociation dynamics of thiophosgene (CSCl2) and the respective branching ratios of both dissociation products Cl and CSCl have been studied by 3D imaging of the photodissociation product chlorine in its ground state 2P3/2[Cl] and excited spin–orbit state 2P1/2[Cl*] employing the resonance enhanced multiphoton ionization and time-of-flight technique at a dissociation wavelength of about 235 nm. A novel technique is applied where the complete three-dimensional (3D) momentum vector of a reaction product is directly determined. The kinetic energy distribution (KED) for Cl* is observed for the first time. The obtained KEDs of Cl and Cl* are different in the low kinetic energy range due to the correlating state of the partner fragment CSCl. In the case of ground state Cl the CSCl partner radical is produced in the ground X, A, and B states with a contribution of 4±0.5%, 60±5%, and 36±3%, respectively. In the case of Cl* the corresponding CSCl is produced with a contribution of 7.5±0.5% in the ground X, 71.5±5.5% in state A, and 21±1.5% in state B. The yield of Cl*, φ(Cl*)=P(Cl*)/[P(Cl)+P(Cl*)], was found to be 0.47. No significant velocity dependence of the anisotropy parameter β could be observed. The mean value +0.03 suggests a decay on the B (A1) surface.

State-to-state rotational energy transfer of ground state NH(X 3Σ−,v=0,J,N) in collisions with He and N2 is studied. A complete inversion between the metastable NH(a 1Δ) state and the NH(X 3Σ−) state is generated via the photodissociation of hydrazoic acid at a wavelength of 266 nm. Single state NH(X 3Σ−,v=0,J,N) is generated by applying the stimulated emission pumping technique using the strongly forbidden NH(a 1Δ→X 3Σ−) intercombination transition around 794 nm. The ground state NH(X 3Σ−,v=0,J,N) distribution is probed with respect to all quantum states using laser induced fluorescence varying delay times and pressures. The collision induced energy transfer between the different rotational and spin levels is extensively studied and two comprehensive sets of rate constants for vibrationally elastic and rotationally inelastic collisions with He and N2 as collision partners are given which include the effect of multiple collisions. We find propensities for (ΔN=0,Δi=±1) and (ΔN=±1,Δi=0) transitions where N ...

The photodissociation dynamics of thionyl chloride are investigated by a one-dimensional resonance enhanced multi-photon/time-of-flight technique (REMPI/TOF) at a dissociation wavelength around 235 nm. Nascent sulfur monoxide molecules and chlorine atoms were detected state-specifically under collision-free conditions for parallel and perpendicular polarisation geometries. Dissociation and detection were performed using the same laser. Polarisation-dependent and state-specific TOF profiles were converted into kinetic energy distributions using a least squares fitting method taking into account velocity-dependent spatial fragment anisotropies. Kinetic energy distributions are narrow and structureless for SO and bimodal for both spin–orbit states of Cl. The bimodality reflects the competition between two- and three-body decay: SOCl2 + hν → SOCl + Cl and SOCl2 + hν → SO + 2 Cl. Chlorine atoms are preferentially released along the polarisation vector of the dissociation laser. The spatial distribution of Cl is characterised by an anisotropy parameter of 0.8 ± 0.2 for the two-body decay and 0.2 ± 0.2 for the three-body decay. SO molecules are isotropically released with low kinetic energy together with two ground state chlorine atoms. These products are most likely to be generated in a sequential three-body decay on a potential energy surface of A′ symmetry. Another surface of A″ symmetry instantaneously produces fast chlorine atoms in a two-body decay process to equal amounts in the ground and the excited spin–orbit states. The corresponding SOCl fragment carries about 50% of the available energy as internal energy.

The photodissociation dynamics of COCl2 has been studied by monitoring ground Cl(2P3/2) and spin–orbit excited Cl*(2P1/2) fragments by applying a novel technique where the three-dimensional momentum vector of a single reaction product is directly determined. The photodissociation at 235 nm produces exclusively three fragments: COCl2+hν→CO+2Cl. The kinetic energy distributions of Cl and Cl* are bimodal and exhibit a different behavior for the different spin–orbit states. Our attention was turned to the dependence of the anisotropy parameter β on the fragment velocity which was observed for the first time. For both spin–orbit states the anisotropy parameter differs clearly for slow and fast chlorine atoms, where a pronounced change from the value ∼0.7 to zero at about 20 kJ/mol is observed. Slow chlorine atoms are released isotropically and predominantly in the ground state Cl whereas fast chlorine atoms have an anisotropy parameter close to the theoretically limiting value and are distributed between groun...

This study is focused on the synthesis and characterization of hydroxy-apo-10'-carotenal/quantum dot (QD) conjugates aiming at the in vivo visualization of β-ionone, a carotenoid-derived volatile compound known for its important contribution to the flavor and aroma of many fruits, vegetables, and plants. The synthesis of nanoparticles bound to plant volatile precursors was achieved via coupling reaction of the QD to C27-aldehyde which was prepared from α-ionone via 12 steps in 2.4% overall yield. The formation of the QD-conjugate was confirmed by measuring its fluorescence spectrum to observe the occurrence of fluorescence resonance energy transfer.

The paper presents experimental and theoretical studies of two-photon excitation dynamics in 2-methyl-5-tert-butyl-p-quaterphenyl (DMQ) dissolved in cyclohexane/paraffin. Experimentally, a two-color two-photon (2C2P) excitation by two femtosecond laser pulses at 800 and 400 nm has been used in combination with the time-resolved detection of polarized molecular fluorescence. The fluorescence decay was found to be two-exponential, resulting in the molecular excited state lifetime of 753 ± 10 ps and the rotational correlation time of 724 ± 45 ps. Control over the excited and fluorescent photons polarization has been used for determination from experiment of seven independent molecular parameters. The experimental data were analyzed on the basis of the recent theoretical approach [Shternin, P. S., Gericke, K.-H., and Vasyutinskii, O. S. Mol. Phys. 2010, 108, 813-825] supported by ab initio computations of the DMQ electronic structure and transition dipole moments. The results obtained imply that the two-photon absorption tensor S is mostly diagonal and that the Szz tensor component onto the molecular long axis gives the major contribution of 93%. However, it was also found that a number of different symmetry two-photon transitions related to the dipole moment components dxdz and dydz are excited in the conditions of our measurements.

The ∼235 nm photodissociation of CH3CFCl2 pre-excited to three, four, and five quanta of C–H methyl stretches was studied to investigate the effect of internal parent excitation on the dynamics of two- and three-body photofragmentation. The ∼235 nm photons also tagged spin-orbit ground Cl 2P3/2 [Cl] and excited Cl 2P1/2 [Cl*] state photofragments, via (2+1) resonantly enhanced multiphoton ionization in a time-of-flight mass spectrometer. Monitoring the shapes of 35Cl and 35Cl* time-of-arrival profiles revealed their energies and angular distributions and showed broad and unstructured fragment kinetic energy distributions. Although a significant amount (∼50%) of the available energy is transferred into internal energy of the CH3CFCl fragment, the spatial Cl distribution is characterized by a nonvanishing anisotropy parameter, β, which indicates at a fast dissociation of the parent molecule along the C–Cl dissociation coordinate. Moreover, β for Cl changes from a slightly positive value to a negative value,...

Excitation of C–H stretch overtones of CHFCl2 followed by ∼235 nm photodissociation was applied to investigate the effect of internal parent excitation on the dynamics of two- and three-body photofragmentation. The ∼235 nm photons also tagged ground Cl 2P3/2 [Cl] and spin–orbit excited Cl 2P1/2 [Cl*] state photofragments, via (2+1) resonantly enhanced multiphoton ionization in a time-of-flight mass spectrometer, and monitored their time-of-arrival profiles. These profiles revealed the product velocities and angular distributions of 35Cl and 35Cl* and suggest the contribution of three-body decay in photodissociation of CHFCl2 pre-excited with five quanta of C–H stretch. This is the first evidence for three-body decay in photodissociation of vibrationally excited molecules.

State-to-state rotational energy transfer of ground state NH(X 3Σ,v=0,J,N) in collisions with Ne is examined. NH is exclusively generated in the metastable NH(a 1Δ) state via photodissociation of hydrazoic acid at a wavelength of 266 nm. The strongly forbidden NH(a 1Δ→X 3Σ−) intercombination transition around 794 nm is used to generate single state NH(X 3Σ−,v=0,J,N) applying the stimulated emission pumping technique. The ground state radicals are detected after a certain delay time with laser induced fluorescence (LIF) using the intense NH(A 3Π←X 3Σ−) transition around 336 nm with respect to all quantum states. The collision induced energy flux between the different rotation and spin levels is studied in detail and a comprehensive set of state-to-state rate constants for inelastic collisions of NH(X 3Σ−,v=0,J,N) with Ne up to N=7 which include the effect of multiple collisions is given. The state-to-state rate constants are obtained by the use of an iterative integrated profiles method. We find a propensi...

At 230 nm, the photodissociation of OCS via a hot band and a triplet state was investigated by selective probing of high rotational levels of product CO (J=45–67) with photofragment imaging spectroscopy: OCS(v=0)+hν(UV)→CO(X 1Σ+,J⩾65)+S(3P), OCS(v=1)+hν(UV) →CO(X 1Σ+,J∼65)+S(1D). Additional two-photon IR excitation of the UV photoprepared OCS with intense 1.06 μm laser pulses bleaches the UV processes listed above and induces a new excitation channel of OCS: OCS(v=0)+hν(UV)→OCS*, OCS*+2hν(IR)→CO(X 1Σ+,J∼74)+S(1S). The bending mode of OCS in the excited states plays a central role in the excitation and dissociation dynamics. Additionally, the alignment effect of OCS by nonresonant infrared laser pulse, which appears on the angular distribution of the photofragment, is discussed.

New experimental techniques and novel analysis procedures promote the investigation of three-body processes. Photoinduced three-body decay can be studied by technologically advanced, challenging coincidence experiments as well as by established spectroscopic techniques if physically meaningful decay mechanisms and parameters are introduced. Such kinematic analysis procedures, based on the evaluation of fragment kinetic energy distributions, are presented, ranging from synchronous concerted via asynchronous concerted to purely sequential decay mechanisms. A Dalitz plot representation of a three-body decay is proffered, bridging the gap between established methods and novel coincidence techniques. Results for structurally similar molecules are presented: phosgene, carbonyl chloride fluoride, and thionyl chloride. Competing mechanisms govern the decay of phosgene via the X 1 A1 ground state and the A 1 A2 excited state potential energy surfaces. Carbonyl chloride fluoride behaves similarly, but the larger stability of the COF intermediate reduces the complexity brought about by decay channel competition and essentially confirms the phosgene results. Two electronic excited states determine the dynamics of the thionyl chloride decay leading to a competition between three- and two-body decay. Fragmentation from the second absorption band leads to results comparable to the phosgene decay via the A 1 A2 state.

A new method is presented to examine state-to-state rotational energy transfer in ground state NH(X 3Σ−,v=0,J,N). NH(X 3Σ−) is generated via state selective stimulated emission pumping using the strongly forbidden NH(a 1Δ→X 3Σ−) intercombination transition around 794 nm after foregoing photodissociation of HN3 at a wavelength of 266 nm. Products are detected by laser induced fluorescence (LIF). Chemically relevant collision dynamics including spatial processes can be studied for the first time in v=0 of the electronic ground state. State-to-state rate constants for inelastic collisions of NH(X 3Σ−,v=0,J=3,N=3) with Ne are presented.

A completely resolved spectrum of the strongly forbidden NH (a(1)Delta --X(3)Sigma(-)) transition is observed. The NH radicals in the excited a(1)Delta state are exclusively generated in a Nd:YAG laser photolysis of hydrazoic acid at a wavelength of 266 nm. The NH (a(1)Delta --X(3)Sigma(-)) intercombination transition around 794 nm is used to produce NH (X(3)Sigma(-)) applying the stimulated emission pumping technique. The ground state radicals are detected by laser-induced fluorescence (LIF). The energy splitting between the NH (X(3)Sigma(-), v = 0, J = 1, N = 0) state and the NH (a(1)Delta, v = 0, J = 2) state is determined with an accuracy of 0.1 cm(-1) to DeltaE = 12 687.8(65) cm(-1). In addition, the radiative lifetime tau of the NH (a(1)Delta --X(3)Sigma(-)) transition was estimated by a determination of the saturation intensity to be tau approximately 12.5 s. Copyright 1999 Academic Press.

The fluorine photodissociation dynamics in the first absorption band was completely characterised by detection of atomic . fluorine using resonantly enhanced multi-photon ionisation REMPI . Jet-cooled parent molecules were excited into the repulsive A 1 P state by a 3s ⁄ 1p electronic transition at 234 nm. Different intermediate excited states of atomic uu g y1 . 1

The photodissociation dynamics of COFCl has been studied by monitoring Cl fragments by resonance enhanced multi-photon ionisation and time-of-flight techniques at dissociation wavelengths near 235 nm. The COFCl heat of formation and the dissociation energy for C–Cl bond fission were for the first time experimentally determined: ΔfH00 (COFCl)=-397±15 kJ mol-1 and D0(COF–Cl)=364±8 kJ mol-1. 35% of the available energy is channelled into FCO rotation and bending vibration. The remaining energy is released as product translation. Other than in phosgene, no spin–orbit state selective behaviour is observed. The observations agree with a decay mechanism within the COFCl molecular plane as well as with a fragmentation via out-of-plane movement of the departing Cl atom. The structural and electronic similarity of COFCl and COCl2 allows conclusions to be drawn on the COCl2 dissociation. The findings are evidence for a previously proposed decay mechanism for the asynchronous concerted three body decay of phosgene into CO+2Cl. The first bond cleavage produces ground and excited spin–orbit state Cl and Cl*, respectively, with large kinetic energy release, while breaking the second C–Cl bond exclusively generates slow ground state Cl atoms.

The time-of-flight spectrum of the H atoms resulting from photodissociation of gas phase HFCO molecules at 243.12 nm indicates a role for secondary photolysis of HCO() fragments arising via the F+HCO() dissociation channel. Analysis of this spectrum, and of earlier photofragment translational spectroscopy results obtained at a number of neighbouring wavelengths in the range 218.4–248.2 nm, allow estimation of an upper limit for the C–F bond dissociation energy: D0(F–CHO)⩽482 kJ mol-1. HCO() fragments are deduced to be amongst the primary products of HFCO photolysis at all wavelengths λ⩽248.2 nm, indicating that any energy barrier in the F–C bond fission channel [measured relative to the asymptotic products F(2P)+HCO()] must be small. This observation is considered in the light of available knowledge regarding the potential energy surfaces for the ground (1A′) and first excited singlet (A1A″) and triplet (a3A″) states of HFCO; the available evidence all points to radiationless transfer and subsequent dissociation on the triplet surface as the mechanism for the deduced F–C bond fission.

The influence of rotation and vibration on the reactivity and the dynamics of the reaction X+HCN(ν1,ν2,ν3,J)→HX+CN(v,J) with X=H, Cl has been studied. The HCN molecule is prepared in a specific rovibrational level by IR/VIS overtone excitation in the wavelength region 6500–18 000 cm−1. The H atoms are generated by laser photolysis of CH3SH at 266 nm, the Cl atoms are formed in the photodissociation of Cl2 at 355 nm. The CN products are probed quantum state specifically by laser-induced fluorescence (LIF). For low rotational states of HCN, the reactivity of Cl and H is independent of the initial rotational state. However, an enhancement in reactivity of the Cl+HCN reaction is observed when the time of rotation becomes comparable to the passing time of the Cl atom. The reaction of Cl as well as of the H atom with HCN shows strong mode specific behavior, implying a simple direct reaction mechanism, which is also supported from Rice–Ramsperger–Kassel–Marcus (RRKM) calculations. An increase in CH stretch vibra...

The photodissociation dynamics of OClO in the near ultraviolet (UV) was investigated in a state specific and energy selective manner. At a dissociation wavelength of 308 nm, OClO(X 2B1) was excited to the OClO(A 2A2(18,0,0)) state, from which it decays into ClO(X 2Π3/2,1/2) and O(3P2,1,0). The nascent oxygen fragments were detected spin selectively by resonant enhanced multiphoton ionization and time of flight measurements (REMPI-TOF). Based on the measurements and the conservation of energy and linear momentum, the internal energy of the ClO partner fragment was obtained. On average, more than 60% of the available energy is transferred into internal excitation of the ClO radical. Nearly the whole internal energy is vibrational energy with vibrational levels populated up to the energetic limit. Besides, the internal energy depends on the oxygen spin-orbit state because the fraction of highly excited ClO fragments increases with increasing total angular momentum J. The bimodal behavior of the fragment ene...

Using polarized light the reaction geometry of selected species can be controlled even in bulk experiments. One reactant A is generated in a photodissociation process and its spatial distribution is completely described by the anisotropy parameter β. The other molecular reactant B is excited in a specific rovibrational state. Its spatial distribution is given by the J- and branch-dependent alignment parameter A0(2). Equations have been developed that allow a relatively easy conversion of experimental results to the angle of attack, γ. The unnormalized probability of an attack of A on B under an angle γ is given by the simple expression P(γ)∝[1+15βA0(2)P2(cos γ)P2(cos δ)] where δ is the angle between the E vectors of the dissociating and the exciting laser beam. As an example, we have studied the reaction of A+HCN→HA+CN with A=H,Cl. The experimental results prove a preferred linear reaction geometry, i.e, an end-on attack of atom A on the terminating hydrogen atom of the HCN reactant. However, the cone of...

The stratospheric trace gas chlorine dioxide diluted in nitrogen at normal pressure is irradiated with laser light at a wavelength of 308 nm, which corresponds essentially to the (X2B10,0,0) → (A2A218,0,0) symmetric stretch progression of OClO. This highly vibrationally excited initial OClO state produces ClO(X2ΠΩ,v,J) radicals containing almost the entire amount of excess energy in their internal degrees of freedom. The ClO fragments resulting from this dissociation process carry sufficient internal energy to exceed the activation energy for the reaction with nitrogen. Accordingly, the reaction ClO(v≫0)+N2 → Cl+N2O could represent an additional source for nitrous oxide and atomic chlorine in the stratosphere. The generation of N2O is experimentally observed in a single-shot laser experiment where the N2O is detected by means of a gas chromatograph. The experimental results indicate that there is in fact a strong evidence for the production of nitrous oxide via the vibrationally mediated reaction of ClO radicals with abundant nitrogen molecules.

The reaction geometry of selected species can be controlled by using polarized light even in bulk experiments. One reactant A is generated in a photodissociation process. Its spatial distribution is completely described by the anisotropy parameter β. The other molecular reactant B is excited in a specific rovibrational state. Its spatial distribution is given by the j- and branch-dependent alignment parameter A0(2). The unnormalized probability of an attack of A on B under an angle γ is then given by the simple expression P(γ) ∝ [1 + 1/5βA0(2)P2(cos γ) P2(cos δ)], where δ is the angle between the E-vectors of the dissociating and of the exciting laser beams. P2(x) represents the second Legendre polynom. We have studied the reaction of X + HCN → HX + CN with X = H, Cl. The attacking H atom is generated in the photodissociation of CH3SH at 266 nm, and the chlorine atom is formed in the photolysis of Cl2 at 355 nm. In both cases the β-parameter is close to −1. In order to align the HCN partner reactant, the...

Faced with the problem of underdetermined kinetic equations in analyzing momenta and kinetic energies of three body decay fragments, we followed two conceptually different paths in order to shed light on the dynamics of the process. One is based on the evaluation of the observed kinematic quantities after introduction of physically meaningful parameters for each type of decay: sequential, synchronously concerted, and asynchronously concerted mechanism. The other one is based on an information theoretic approach, maximizing the entropy of the joint probability matrix containing the probabilities for coincidently realizing accessible sets of product states. The results obtained in both cases match remarkably well: No significant contribution of a molecular channel, producing chlorine molecules, was found. Likewise, the generation of a stable chloroformyl radical had been ruled out in previous studies, so that every dissociation process upon irradiation around 230 nm yields three fragments: two chlorine a...

The photo induced three body decay : ABC hnu A B C, where a molecule ABC decays into three fragments A, B and C upon irradiation, is reviewed. Various experimental and theoretical techniques for the investigation of this reaction and their application to a wide range of molecular species are discussed. Emphasis is laid on the distinction between concerted and stepwise processes, consisting of one single or two consecutive kinetic events, respectively. The concerted fragmentation scheme is further classified as being of either synchronous or asynchronous character, depending on whether or not the bond breaking processes take place in unison. The three body decays of acetone, azomethane and s-tetrazine are discussed in detail as prototypes for these mechanisms. A novel kinematic analysis approach, based on the evaluation of fragment kinetic energy distributions, is presented and applied to the ultraviolet photodissociation of phosgene. Competing pathways are found to be operative, dominated by the asynchron...

Vibrational overtone excitation of HCN in the wavelength region 6 500 cm−1–18 000 cm−1 is used to initiate the endothermic reaction of chlorine and hydrogen atoms with HCN. HCN is excited to the overtone levels (002), (004), (302), (105), and (1115). The labeling of the vibrational levels (ν1ν2l2ν3) corresponds to the normal modes ν1=CN, ν2=bend, ν3=CH, and l2=vibrational angular momentum. The product state distribution of CN(X 2Σ+) is completely analyzed by laser induced fluorescence (LIF). Excitation of the first overtone of CH‐stretch leads to vibrationally excited CN in the reaction of Cl+HCN(002), implying the existence of a long living complex. The CN vibrational excitation increases with increasing H–CN stretch excitation. However, a slightly higher CN vibrational excitation is found when at the same internal energy of HCN three quanta of CN‐stretch and two quanta of CH‐stretch are excited. Therefore, the energy is not completely redistributed in the collision complex. The ratio of rate constants b...

Applying the two‐photon laser‐induced fluorescence technique for nascent state resolved ClO(X 2ΠΩ,v,J) detection, the photofragmentation dynamics of OClO in the (A 2A211,0,0) and the (A 2A218,0,0) state is investigated at fixed photolysis wavelengths of 351 nm and 308 nm. In both experiments the product fragments are formed in their electronic ground states, namely ClO(2ΠΩ) and O(3P). A complete product state analysis proves the ClO radicals originating from the OClO(A 2A211,0,0) dissociation at 351 nm to be formed in v=0–4 vibrational states with a spin–orbit ratio of P(2Π3/2):P(2Π1/2)=3.8±0.5. The ClO fragment shows moderate rotational excitation. The obtained ClO product state distributions and the relatively high translational energy of the fragments can be explained by predissociation of the (A 2A2ν1,0,0)‐excited parent molecule in the course of which the initial symmetric stretch motion (ν1) of OClO is transferred into the dissociative asymmetric stretching mode (ν3). ClO line profile measuremen...

We present the results of theoretical and experimental studies of the polarized fluorescence in fluorophores excited by two-photon two-color (2P2C) femtosecond laser pulses. Quantum mechanical expressions describing the fluorescence polarization have been derived using the spherical tensor technique for asymmetric top molecules under the condition of isotropic rotation diffusion for arbitrary polarization of each of the three photons involved in the photoprocess. The expressions are presented in terms of the molecular parameters MK(R, R´, t) which contain all information about the photoprocess dynamics and can be directly determined from experiment. Ab initio computations of the flurophore structure and two-photon dynamics have been performed for p-terphenyl and indole in vacuum and in solutes using the polarizable continuum model and TD-DFT method, respectively. In case of p-terphenyl, full geometry optimization of the low-lying excited singlet electronic of the D2h symmetry has been performed. The results obtained indicate that that the solute molecules do not affect noticeably the position of the p-terphenyl energy levels which conclusion nicely fits the results reported elsewhere. In case of indole, the energy of low-lying molecular states, their permanent dipole moments, and transition dipole moments to the ground state have been computed both for non-relaxed and relaxed geometries. The results obtained manifests strong influence of the polar solute (methanol) on the position of the lowlying molecular energy levels and on the dipole moments. Using the results of the computation obtained three molecular parameters of the zero-th order, M0(0,0), M0(2,0), M0(2,2) have been calculated and compared with their values obtained experimentally. The comparison shows excellent agreement between the theory and experiment.

The ultraviolet photodissociation of phosgene in its first absorption band 1A2←1A1 was investigated by resonance enhanced multiphoton ionization and time of flight techniques. Nascent atomic chlorine fragments were observed and their state specific kinetic energy distributions were determined. Of the chlorine atoms 15% are produced in the excited 2P1/2 spin–orbit state with a mean kinetic energy of 3200 cm−1 compared to a value of 1500 cm−1 for the mean kinetic energy of the ground state chlorine atoms. The analysis of the kinetic energy spectra yielded evidence for a concerted three‐body decay. The formation of intermediate COCl is of minor importance in the dissociation process, the formation of a stable final COCl product can be excluded. Competing pathways on the upper potential energy surface are discussed. A significant excitation of the carbon monoxide CO fragments is predicted.

Modified hydroxyethyl starch is photo-crosslinked in the presence of a green fluorescent protein (GFP) (mTagGFP) to obtain loaded hydrogels as model for a drug-delivery system. An important factor for the protein release is the crosslinking density since a dense network should lead to hindered diffusion. To obtain information on the rotational and translational diffusion of GFP in the hydrogel, mTagGFP is analyzed by fluorescence anisotropy and fluorescence recovery after photo-bleaching experiments using two-photon excitation. The mTagGFP shows a viscosity-retarded rotational and strongly hindered translational diffusion, depending on the polymer concentration. A comparison of anisotropy studies with mTagGFP-loaded microparticles and hydrogel disks allows the polymer concentration to be determined for the microparticles, which has been previously unknown.