Average Rotational Energy Research Articles

NO (A) Rotational State Distributions from Photodissociation of the N2-NO Complex.

We have recorded the resonance-enhanced multiphoton ionization spectrum for NO (A) products from photodissociation of the N2-NO complex. We made measurements at excitation energies ranging from 28 to 758 cm-1 above the threshold to produce NO (A) + N2 (X) products, and the resulting spectra reveal the NO (A) rotational states formed during dissociation, allowing us to determine the rotational state distribution. At the lowest available energies, 28 and 50 cm-1 above threshold, we observed contributions from NO (A) rotational states that exceed the available energy and must originate from excitation due to hotbands of the complex. At all higher energies, we did not observe any energetically disallowed NO (A) rotational states, and for all available energies above 259 cm-1 the observed rotational transitions do not extend to the maximum allowed by energy conservation. Furthermore, the observed distributions were typically biased toward low rotational states, in contrast with expectations from vibrational predissociation. From the rotational state distributions, we determined the average fraction of energy partitioned into NO (A) rotation, fNOrot,ave, to be 0.088 at the highest available energy, and this fraction increased as the available energy decreased. By combining the average NO (A) rotational energy along with the average center-of-mass translational energy from our previous work, we determined the average rotational energy for the undetected N2 (X) photoproduct. The results showed that the N2 fragment has a higher average rotational energy relative to the NO fragment. Finally, we found that the NO (A) rotational state distribution was colder than expected for a statistical dissociation.

Numerical study of the dynamic behaviour of iron ore particles during wet granulation process using discrete element method

Iron ore granulation process is simulated by the discrete element method to understand the dynamic behaviour of iron ore particles. The results show that the macroscopic particle flow transits from rolling regime to cascading regime after water addition, with the angle of repose of particles increasing and the level of particle size segregation decreasing. The moisture distribution becomes more uniform through particle tumbling, which improves the granule growth. The microdynamic behaviours of the fines, intermediates and nuclei during the auto-layering process have been studied respectively. The variations in the average contact number, kinetic and rotational energy per particle with granulation time are analysed. The optimal moisture contents for Ores N, M and Y are estimated as 6.46 wt%, 9.12 wt% and 8.70 wt%, respectively. The numerical results are generally in accordance with the corresponding experimental ones, which basically validates the DEM modelling of iron ore granulation presented in this paper.

Infrared Emission from Photodissociation of Methyl Formate [HC(O)OCH3] at 248 and 193 nm: Absence of Roaming Signature.

Following photodissociation at 248 nm of gaseous methyl formate (HC(O)OCH3, 0.73 Torr) and Ar (0.14 Torr), temporally resolved vibration-rotational emission spectra of highly internally excited CO (ν ≤ 11, J ≤ 27) in the 1850-2250 cm-1 region were recorded with a step-scan Fourier-transform spectrometer. The vibration-rotational distribution of CO is almost Boltzmann, with a nascent average rotational energy (ER0) of 3 ± 1 kJ mol-1 and a vibrational energy (EV0) of 76 ± 9 kJ mol-1. With 3 Torr of Ar added to the system, the average vibrational energy was decreased to EV0 = 61 ± 7 kJ mol-1. We observed no distinct evidence of a bimodal rotational distribution for ν = 1 and 2, as reported previously [Lombardi et al., J. Phys. Chem. A 2016, 129, 5155], as evidence of a roaming mechanism. The vibrational distribution with a temperature of ∼13000 ± 1000 K, however, agrees satisfactorily with trajectory calculations of these authors, who took into account conical intersections from the S1 state. Highly internally excited CH3OH that is expected to be produced from a roaming mechanism was unobserved. Following photodissociation at 193 nm of gaseous HC(O)OCH3 (0.42 Torr) and Ar (0.09 Torr), vibration-rotational emission spectra of CO (ν ≤ 4, J ≤ 38) and CO2 (with two components of varied internal distributions) were observed, indicating that new channels are open. Quantum-chemical calculations, computed at varied levels of theory, on the ground electronic potential-energy schemes provide a possible explanation for some of our observations. At 193 nm, the CO2 was produced from secondary dissociation of the products HC(O)O and CH3OCO, and CO was produced primarily from secondary dissociation of the product HCO produced on the S1 surface or the decomposition to CH3OH + CO on the S0 surface.

Effect of mill speed and slurry filling on the charge dynamics by an instrumented ball

In the ball mill, the motion of charge is a complex system, especially under wet grinding. It is difficult to measure the charge physical quantities and hard to validate the correctness of charge motion simulation. To this end, an instrumented ball which is capable of measuring the charge physical quantities was designed. The laboratory ball mill was lined with 12 pieces of trapezium lifters and filled with Jb = 25% grinding balls. An iron ore was used to prepare the slurry at 50% solid concentration by mass. A series of tests were carried out to investigate the charge dynamics at different mill speeds and slurry filling. The average rotational kinetic energy, average applied force and mill power were measured and analyzed. The results showed that the average rotational kinetic energy increases with mill speed, whereas the average applied force first increases and then decreases. The average rotational kinetic energy and applied force first increases and then decreases by the increase in slurry filling. Furthermore, there exists a slurry filling U = U* that the mill power has a maximum value.

Translational, rotational and vibrational relaxation dynamics of a solute molecule in a non-interacting solvent.

Spectroscopically observing the translational and rotational motion of solute molecules in liquid solutions is typically impeded by their interactions with the solvent, which conceal spectral detail through linewidth broadening. Here we show that unique insights into solute dynamics can be made with perfluorinated solvents, which interact weakly with solutes and provide a simplified liquid environment that helps to bridge the gap in our understanding of gas- and liquid-phase dynamics. Specifically, we show that in such solvents, the translational and rotational cooling of an energetic CN radical can be observed directly using ultrafast transient absorption spectroscopy. We observe that translational-energy dissipation within these liquids can be modelled through a series of classic collisions, whereas classically simulated rotational-energy dissipation is shown to be distinctly faster than experimentally measured. We also observe the onset of rotational hindering from nearby solvent molecules, which arises as the average rotational energy of the solute falls below the effective barrier to rotation induced by the solvent.

Two HCl-Elimination Channels and Two CO-Formation Channels Detected with Time-Resolved Infrared Emission upon Photolysis of Acryloyl Chloride [CH2CHC(O)Cl] at 193 nm

Following photodissociation of gaseous acryloyl chloride, CH2CHC(O)Cl, at 193 nm, temporally resolved vibration-rotational emission spectra of HCl (v ≤ 7, J ≤ 35) in region 2350-3250 cm(-1) and of CO (v ≤ 4, J ≤ 67) in region 1865-2300 cm(-1) were recorded with a step-scan Fourier-transform spectrometer. The HCl emission shows a minor low-J component for v ≤ 4 with average rotational energy Erot = 9 ± 3 kJ mol(-1) and vibrational energy Evib = 28 ± 7 kJ mol(-1) and a major high-J component for v ≤ 7 with average rotational energy Erot = 36 ± 6 kJ mol(-1) and vibrational energy Evib = 49 ± 9 kJ mol(-1); the branching ratio of these two channels is ∼0.2:0.8. Using electronic structure calculations to characterize the transition states and each intrinsic reaction coordinate, we find that the minor pathway corresponds to the four-center HCl-elimination of CH2ClCHCO following a 1,3-Cl-shift of CH2CHC(O)Cl, whereas the major pathway corresponds to the direct four-center HCl-elimination of CH2CHC(O)Cl. Although several channels are expected for CO produced from the secondary dissociation of C2H3CO and H2C═C═C═O, each produced from two possible dissociation channels of CH2CHC(O)Cl, the CO emission shows a near-Boltzmann rotational distribution with average rotational energy Erot = 21 ± 4 kJ mol(-1) and average vibrational energy Evib = 10 ± 4 kJ mol(-1). Consideration of the branching fractions suggests that the CO observed with greater vibrational excitation might result from secondary decomposition of H2C═C═C═O that was produced via the minor low-J HCl-elimination channel, while the internal state distributions of CO produced from the other three channels are indistinguishable. We also introduce a method for choosing the correct point along the intrinsic reaction coordinate for a roaming HCl elimination channel to generate a Franck-Condon prediction for the HCl vibrational energy.

UV photochemistry of peroxyformic acid (HC(O)OOH): an experimental and computational study investigating 355 nm photolysis.

The photochemistry of peroxyformic acid (PFA), a molecule of atmospheric interest exhibiting internal hydrogen bonding, is examined by exciting the molecule at 355 nm and detecting the nascent OH fragments using laser-induced fluorescence. The OH radicals are found to be formed in their ground electronic state with the vast majority of available energy appearing in fragment translation. The OH fragments are vibrationally cold (v" = 0) with only modest rotational excitation. The average rotational energy is determined to be 0.35 kcal/mol. Further, the degree of OH rotational excitation from PFA is found to be significantly less than that arising from the dissociation of H2O2 as well as other hydroperoxides over the same wavelength. Ab initio calculation at the EOM-CCSD level is used to investigate the first few electronic excited states of PFA. Differences in the computed torsional potential between PFA and H2O2 help rationalize the observed variation in their respective OH fragment rotational excitation. The calculations also establish that the electronic excited state of PFA accessed in the near UV is of (1)A" symmetry and involves a σ*(O-O) ← n(O) excitation. Additionally, the UV absorption cross section of PFA at 355 and 282 nm is estimated by comparing the yield of OH from PFA at these wavelengths to that from hydrogen peroxide for which the absorption cross sections is known.

Early time detection of OH radical products from energized Criegee intermediates CH2OO and CH3CHOO

The OH radical products from unimolecular decay of energized CH2OO and CH3CHOO Criegee intermediates are detected by laser-induced fluorescence shortly after they are formed utilizing 248nm photolysis of diiodo precursors and subsequent reaction with O2. The OH radicals from both CH2OO and CH3CHOO are produced with average rotational energies of ∼1–2kcalmol−1. A different mechanism for unimolecular decay of CH3CHOO is evident from noticeably broader OH A-X (1,0) line profiles, which is attributed to Doppler broadening. Modeling of the Doppler profiles suggests that most of the available energy is channeled into translational excitation of the products.

Evolution of the Reorientational Motions of the Tetrahydroborate Anions in Hexagonal LiBH4–LiI Solid Solution by High-Q Quasielastic Neutron Scattering

The reorientational dynamics of tetrahydroborate (BH4–) anions in the hexagonal 1:1 LiBH4–LiI solid solution were characterized by quasielastic neutron scattering (QENS) with results extended to high momentum transfers (Q). Measurements are compared in detail to results for LiBH4 and to a range of models describing the various possible reorientational mechanisms. The high reorientational mobility compared to that for BH4– in other solid-state environments reflects a favorable combination of the underlying hexagonal close-packed lattice and the unusually large BH4– crystallographic site stabilized by the presence of the I– anions throughout the structure. QENS data up to momentum transfers of 4.2 Å–1 at 125 K reveal a dominant uniaxial reorientation mechanism consisting of rapid BH4– diffusive-like rotational motions of three H atoms in a ring around the c-directed trigonal B–H axis, with the fourth axial H atom remaining stationary. By 200 K, this diffusive ring of three H atoms undergoes noticeable jump exchanges with the axial H atom, identical to what has been observed for BH4– reorientations in hexagonal LiBH4 at much higher temperature. The two separate mechanisms are consistent with the two reorientational motions revealed recently by NMR measurements. An average rotational activation energy of 36 meV ± 1 meV is derived over a wide temperature range.

State-resolved master equation analysis of thermochemical nonequilibrium of nitrogen

Using a NASA database of state-to-state transition rates for N+N2, master equation studies are performed for various nonequilibrium heat bath conditions. In these master equation studies, relaxation of the rotational and vibrational modes, time variation of chemical composition, reaction rate coefficients, and average rotational and vibrational energy losses due to dissociation are each considered in strong and weak nonequilibrium conditions. A system of master equations is coupled with one-dimensional flow equations to analyze the relaxation of N2 in post-normal shock flows. From the results of master equations and the post-normal shock calculations, it is recommended that the rotational nonequilibrium of N2 should be treated as a nonequilibrium mode in hypersonic re-entry calculations.

State-resolved thermochemical nonequilibrium analysis of hydrogen mixture flows

The complete sets of state-to-state transition rate coefficients for both target and projectile molecules of hydrogen are derived from the predicted response surface designed by the ordinary Kriging model. A system of master equations is constructed for bound-bound and bound-free transitions with these designed transition rate coefficients, and the rovibrational number densities are numerically evaluated by implicitly integrating a system of master equations. In these master equation studies, relaxation of rotation and vibration modes, number density relaxation, reaction rate coefficients, and average rotational and vibrational energy losses due to dissociation are each considered in strong nonequilibrium conditions. A system of master equations is coupled with one-dimensional flow equations to analyze the relaxations of hydrogen in post-normal shock and nozzle expanding flows. In post-normal shock flows, at high temperature, the relaxation of the rotational mode is similar to the relaxation of the vibrational mode. In nozzle expanding flows, the relaxations of both rotational and vibrational modes appear to be frozen.

Vibrational relaxation and vibration-rotation energy transfer between highly vibrationally excited KH(X1Σ+, v=14–21) and CO2

The vibrational levels of KH(X1Σ+, v″=0–3) were generated in the reaction of K (5P) and H2. Vibrational state total relaxation rate coefficientskv″(CO2) for KH (v″=14–21) are measured in an overtone pump-probe configuration. The rate coefficient kv″(CO2) is strongly dependent on vibrational quantum number. Scattered CO2 (0000, 32≤J≤48) molecules were excited to CO2 (1005, J+1) states. The rotational temperatures of CO2 (0000, J=32–48) states populated by collisions with highly vibrationally excited KH (v″=14–21) are obtained. The average rotational energy of the scattered CO2 molecules is increased by a factor of 2.33 when KH level v″=14 increases to v″=21. The average translational energy of the scattered CO2 molecules is increased roughly linearly as a function of CO2J state. Under single collision conditions, state-specific energy transfer rate coefficients for collisions of highly excited KH with CO2 are obtained. For v″=19, the integrated rate coefficients kint increases by a factor of 4.5 to v″=14.

Dynamics of collisions of hydroxyl radicals with fluorinated self-assembled monolayers

We present a classical trajectory study of the dynamics of collisions between OH radicals and fluorinated self-assembled monolayers (F-SAMs). The gas/surface interaction potential required in the simulations has been derived from high-level ab initio calculations (focal-point-CCSD(T)/aug-cc-pVQZ) of various approaches of OH to a model fluorinated alkane. The two lowest-energy doublet potential energy surfaces considered in the electronic structure calculations have been averaged to produce a pairwise analytic potential. This analytic potential has been subsequently employed to propagate classical trajectories of collisions between OH and F-SAMs at initial conditions relevant to recent experiments on related systems. The calculated rotational distributions of the inelastically scattered OH agree well with the experiment, which serves to validate the accuracy of the simulations. Investigation of the dynamics of energy transfer for different initial rotational states of OH indicates that an increase in the initial rotation of OH results in increases in both the final average OH rotational and translational energy and in a slight decrease in the amount of energy transferred to the surface. Analysis of the dynamics as a function of the desorption angle of OH from the surface shows that while there is a correlation between the final scattering angle and OH’s amount of final translational energy, the amount of rotational energy in OH is largely independent of the desorption angle. The mechanism of the collisions is found to be mostly direct; in about 90% of most trajectories, OH only collides with the surface once before desorbing, which exemplifies the rigidity of fluorinated monolayer surfaces and their inability to efficiently accommodate gas species.

Photodissociation Dynamics of Benzaldehyde (C6H5CHO) at 266, 248, and 193 nm

The photodissociation of gaseous benzaldehyde (C(6)H(5)CHO) at 193, 248, and 266 nm using multimass ion imaging and step-scan time-resolved Fourier-transform infrared emission techniques is investigated. We also characterize the potential energies with the CCSD(T)/6-311+G(3df,2p) method and predict the branching ratios for various channels of dissociation. Upon photolysis at 248 and 266 nm, two major channels for formation of HCO and CO, with relative branching of 0.37:0.63 and 0.20:0.80, respectively, are observed. The C(6)H(5)+HCO channel has two components with large and small recoil velocities; the rapid component with average translational energy of approximately 25 kJ mol(-1) dominates. The C(6)H(6)+CO channel has a similar distribution of translational energy for these two components. IR emission from internally excited C(6)H(5)CHO, ν(3) (v=1) of HCO, and levels v≤2, J≤43 of CO are observed; the latter has an average rotational energy of approximately 13 kJ mol(-1) and vibrational energy of approximately 6 kJ mol(-1). Upon photolysis at 193 nm, similar distributions of energy are observed, except that the C(6)H(5)+HCO channel becomes the only major channel with a branching ratio of 0.82±0.10 and an increased proportion of the slow component; IR emission from levels ν(1) (v=1) and ν(3) (v=1 and 2) of HCO and v≤2, J≤43 of CO are observed; the latter has an average energy similar to that observed in photolysis at 248 nm. The observed product yields at different dissociation energies are compared to statistical-theory predicted results based on the computed singlet and triplet potential-energy surfaces.

XUV Free-Electron Laser Desorption of NO from Graphite (0001)

We report results of femtosecond laser induced desorption of NO from highly oriented pyrolytic graphite using XUV photon energies of hν = 38 eV and hν = 57 eV. Femtosecond pulses with a pulse energy of up to 40 μJ and about 30 fs duration generated at FLASH are applied. The desorbed molecules are detected with rovibrational state selectivity by (1 + 1) REMPI in the A(2)Σ(+) ← X(2)Π γ-bands around λ = 226 nm. A nonlinear desorption yield of neutral NO is observed with an exponent of m = 1.4 ± 0.2. At a fluence of about 4 mJ/cm(2) a desorption cross section of σ(1) = (1.1 ± 0.4) × 10(-17) cm(2) is observed, accompanied with a lower one of σ(2) = (2.6 ± 0.3) × 10(-19) cm(2) observable at higher total fluence. A nonthermal rovibrational population distribution is observed with an average rotational energy of <E(rot)> = 38.6 meV (311 cm(-1)), a vibrational energy of <E(vib)> = 136 meV (1097 cm(-1)) and an electronic energy of <E(el)> = 3.9 meV (31 cm(-1)).

Collisional quenching of OD AΣ2+ by H2: Experimental and theoretical studies of the state-resolved OD XΠ2 product distribution and branching fraction

We report joint experimental and theoretical studies of outcomes resulting from the nonreactive quenching of electronically excited OD A (2)Σ(+) by H(2). The experiments utilize a pump-probe technique to detect the OD X (2)Π product state distribution under single collision conditions. The OD X (2)Π products are observed primarily in their lowest vibrational state (v(") = 0) with substantially less population in v(") = 1. The OD X (2)Π products are generated with a high degree of rotational excitation, peaking at N(") = 21 with an average rotational energy of 4600 cm(-1), and a strong propensity for populating the Π(A(')) Λ-doublet component indicative of alignment of the half-filled pπ orbital in the plane of OD rotation. Branching fraction measurements show that the nonreactive channel accounts for less than 20% of quenching outcomes. Complementary classical trajectory calculations of the postquenching dynamics are initiated from representative points along seams of conical intersections between the ground and excited-state potentials of OD(A (2)Σ(+),X (2)Π) + H(2). Diabatic modeling of the initial momenta in the dynamical calculations captures the key experimental trends: OD X (2)Π products released primarily in their ground vibrational state with extensive rotational excitation and a branching ratio that strongly favors reactive quenching. The OD A (2)Σ(+) + H(2) results are also compared with previous studies on the quenching of OH A (2)Σ(+) + H(2); the two experimental studies show remarkably similar rotational energy distributions for the OH and OD X (2)Π radical products.

An improved PTV technique to evaluate the velocity field of non-spherical particles

In recent years, Particle Tracking Velocimetry (PTV) has been extensively used to measure the translational velocity field of granular assemblies in applications such as vibrated beds, rotating drums and Couette shear cells. However, this technique has not yet been shown to be able to determine the velocity field of non-spherical particles. The aim of this paper is to develop an improved PTV technique to determine translational and rotational velocities for non-spherical particles. To prove the feasibility of this new PTV technique, it was employed to investigate the convection behaviour of non-spherical particles in a vibrated bed. In the demonstration example, paired POM particles made by gluing two single POM beads were studied. The test example was a single layer quasi-2D model. The transport properties of the paired POM particles in a vibrated bed, such as local average velocities, local fluctuation velocities, granular temperatures, fluctuation velocity distributions, self-diffusion coefficients and dimensionless convection flow rates, were evaluated from the experimental results and discussed. The developed improved PTV technique is shown to have the ability to measure more accurately the velocity field of non-spherical particulate systems. The study has demonstrated the convection phenomenon of non-spherical particles in a vibrated bed and has shown that particle rotation is significant in the vibrated granular bed. In such a granular system with convection phenomenon, the average rotational kinetic energy constitutes approximately 5.4% of the average kinetic energy and in some local regions the rotational granular temperature amounts to over 17% of the total granular temperature.

Shock-induced melting of (100)-oriented nitromethane: Energy partitioning and vibrational mode heating

A study of the structural relaxation of nitromethane subsequent to shock loading normal to the (100) crystal plane performed using molecular dynamics and a nonreactive potential was reported recently [J. Chem. Phys. 131, 064503 (2009)]. Starting from initial temperatures of T(0)=50 and 200 K, shocks were simulated using impact velocities U(p) ranging from 0.5 to 3.0 km s(-1); clear evidence of melting was obtained for shocks initiated with impacts of 2.0 km s(-1) and higher. Here, we report the results of analyses of those simulation data using a method based on the Eckart frame normal-mode analysis that allows partitioning of the kinetic energy among the molecular degrees of freedom. A description of the energy transfer is obtained in terms of average translational and rotational kinetic energies in addition to the rates of individual vibrational mode heating. Generally, at early times postshock a large superheating of the translational and rotational degrees of freedom (corresponding to phonon modes of the crystal) is observed. The lowest frequency vibrations (gateway modes) are rapidly excited and also exhibit superheating. Excitation of the remaining vibrational modes occurs more slowly. A rapid, early excitation of the symmetric C-H stretch mode was observed for the shock conditions T(0)=50 K and U(p)=2.0 km s(-1) due to a combination of favorable alignment of molecular orientation with the shock direction and frequency matching between the vibration and shock velocity.

Master Equation Study and Nonequilibrium Chemical Reactions for H + H2 and He + H2

Complete sets of state-to-state cross sections and rate coefficients for the transition of 348 (v,j) rotational and vibrational states ofthe electronic ground state of the hydrogen molecule for H and He collisions were evaluated using quasi-classical trajectory calculations based on the latest potential energy surfaces. The state-to-state cross sections for the rotational and vibrational energy transitions were validated by comparing the results with those of quantum mechanical calculations and other quasi-classical trajectory calculations. The state-to-state rate coefficients were fed into a master equation, and the rotational and vibrational number densities were numerically evaluated. In this master equation study, relaxation of the rotational and vibrational temperatures, number density relaxation, and average rotational and vibrational energy losses due to dissociation were examined in heating and cooling environments. From the results of the state-to-state rate coefficients and the master equation study, dissociation and recombination rate coefficients were calculated under a quasi-steady-state assumption for a temperature range between 1000 and 32,000 K. These rate coefficients were validated by comparing the results with existing experiments. The reaction rates expressed by a two-temperature model based on translational and vibrational temperatures were also proposed upon collision with H and He, respectively.

Quantum State Distribution of the OH X2Π Products from Collisional Quenching of OH A2Σ+ by O2 and CO2

The OH X(2)Pi product state distribution arising from quenching of electronically excited OH A(2)Sigma(+) by O(2) and CO(2) under single collision conditions has been determined using a pump-probe technique. For both collision partners, the majority of OH X(2)Pi products are observed in their lowest vibrational level, v'' = 0, with significantly less population in v'' = 1. The OH products from quenching by O(2) are generated with a substantial degree of rotational excitation, peaking around N'' approximately = 17, with an average rotational energy of approximately 4800 cm(-1), whereas OH products from quenching by CO(2) exhibit a moderate degree of rotational excitation, peaking around N'' approximately = 5, with an average rotational energy of approximately 1800 cm(-1). The branching fraction into OH X(2)Pi products states reveals that nonreactive quenching is a significant decay pathway for both systems, accounting for at least 40(1)% of the quenched products with O(2) and 64(5)% with CO(2).