Population Of Rotational Levels Research Articles

Rotational state-to-state transition rate coefficients for H2O + H2O collisions at nonequilibrium conditions

The goal is to develop a database of rate coefficients for rotational state-to-state transitions in H$_ $O + H$_ $O collisions that is suitable for the modeling of energy transfer in nonequilibrium conditions, in which the distribution of rotational states of H$_ $O deviates from local thermodynamic equilibrium. A two-temperature model was employed that assumed that although there is no equilibrium between all possible degrees of freedom in the system, the translational and rotational degrees of freedom can be expected to achieve their own equilibria independently, and that they can be approximately characterized by Boltzmann distributions at two different temperatures, $T_ kin $ and $T_ rot Upon introducing our new parameterization of the collisional rates, taking into account their dependence on both $T_ kin $ and $T_ rot $, we find a change of up to 20<!PCT!> in the H$_ $O rotational level populations for both ortho and para-H$_ $O for the part of the cometary coma where the nonequilibrium regime occurs.

Revisiting the rovibrational (de-)excitation of molecular hydrogen by helium

Context. The collisional (de-)excitation of H2 by He plays an important role in the thermal balance and chemistry of various astro-physical environments, making accurate rate coefficients essential for interpreting observations of the interstellar medium. Aims. Our goal is to utilize a state-of-the-art potential energy surface (PES) to provide comprehensive state-to-state rate coefficients for He-induced transitions among rovibrational levels of H2. Methods. We performed quantum scattering calculations for the H2-He system. Thus, we were able to provide state-to-state rate coefficients for 1059 transitions between rovibrational levels of H2, with internal energies up to ≃15 000 cm−1, for temperatures ranging from 20 to 8000 K. Results. Our results demonstrate a good agreement with previous calculations for pure rotational transitions between low-lying rotational levels. However, we do find significant discrepancies for rovibrational processes involving highly-excited rotational and vibrational states. We attribute these differences to two key factors: (1) the broader range of intramolecular distances covered by ab initio points and (2) the superior accuracy of the PES, resulting from the utilization of the state-of-the-art quantum chemistry methods, compared to previous lower-level calculations. Conclusions. Radiative transfer calculations performed with the new collisional data indicate that the population of rotational levels in excited vibrational states experiences significant modifications, highlighting the critical need for this updated dataset in models of high-temperature astrophysical environments.

Topological Charges of Periodically Kicked Molecules.

We show that the simplest of existing molecules-closed-shell diatomics not interacting with one another-host topological charges when driven by periodic far-off-resonant laser pulses. A periodically kicked molecular rotor can be mapped onto a "crystalline" lattice in angular momentum space. This allows us to define quasimomenta and the band structure in the Floquet representation, by analogy with the Bloch waves of solid-state physics. Applying laser pulses spaced by 1/3 of the molecular rotational period creates a lattice with three atoms per unit cell with staggered hopping. Within the synthetic dimension of the laser strength, we discover Dirac cones with topological charges. These Dirac cones, topologically protected by reflection and time-reversal symmetry, are reminiscent of (although not equivalent to) that seen in graphene. They-and the corresponding edge states-are broadly tunable by adjusting the laser strength and can be observed in present-day experiments by measuring molecular alignment and populations of rotational levels. This paves the way to study controllable topological physics in gas-phase experiments with small molecules as well as to classify dynamical molecular states by their topological invariants.

Laser Probing of the Rotational Cooling of Molecular Ions by Electron Collisions.

We present state-selected measurements of rotational cooling and excitation rates of CH^{+} molecular ions by inelastic electron collisions. The experiments are carried out at a cryogenic storage ring, making use of a monoenergetic electron beam at matched velocity in combination with state-sensitive laser dissociation of the CH^{+} ions for simultaneous monitoring of the rotational level populations. Employing storage times of up to 600s, we create conditions where electron-induced cooling to the J=0 ground state dominates over radiative relaxation, allowing for the experimental determination of inelastic electron collision rates to benchmark state-of-the-art theoretical calculations. On a broader scale, our experiments pave the way to probe inelastic electron collisions for a variety of molecular ions relevant in various plasma environments.

Effect of Reagent Vibration and Rotation on the State-to-State Dynamics of the Hydrogen Exchange Reaction, H + H2 → H2 + H.

State-to-state dynamics of the benchmark hydrogen exchange reaction H + H2 (v = 0-4, j = 0-3) → H2 (v', j') + H is investigated with the aid of the real wave packet approach of Gray and Balint-Kurti (J. Chem. Phys. 1998, 108, 950-962) and electronic ground BKMP2 potential energy surface of Boothroyd et al. (J. Chem. Phys. 1996, 104, 7139-7152). Initial state-selected and product state-resolved reaction probabilities, integral cross section, and product diatom vibrational and rotational level populations at a few collision energies are reported to elucidate the energy disposal mechanism. State-specific thermal rate constants are also calculated and compared with the available literature results. Coriolis coupling terms of the nuclear Hamiltonian are included, and calculations are parallelized over the helicity quantum number, Ω'. Attempts are made, in particular, to study the effect of reagent vibrational and rotational excitations on the dynamical attributes. It is found that the calculations become computationally expensive with reagent vibrational and rotational excitation. Reagent vibrational excitation is found to enhance the reactivity and has significant impact on the energy disposal to the vibrational and rotational degrees of freedom of the product. The interplay of reagent translational and vibrational energy on the product vibrational distribution unfolds an important aspect of the energy disposal mechanism. The effect of reagent rotation on the state-to-state dynamics is found not to be very significant, and the weak effect turns out to be specific to v'.

Physical conditions in the diffuse interstellar medium of local and high-redshift galaxies: measurements based on the excitation of H2 rotational and C i fine-structure levels

ABSTRACT We present the results of an analysis of the physical conditions (number density, intensity of UV field, kinetic temperature) in the cold H2-bearing interstellar medium of local and high-redshift galaxies. Our measurements are based on the fit to the observed population of H2 rotational levels and C i fine-structure levels with the help of grids of numerical models calculated with the photon-dominated region (PDR) Meudon code. A joint analysis of low H2 rotational levels and C i fine-structure levels breaks the degeneracy in the IUV−nH plane and provides significantly tighter constraints on the number density and intensity of the UV field. Using archive data from the VLT/UVES, KECK/HIRES, HST/STIS and FUSE telescopes, we selected 12 high-redshift damped Lyα systems (DLAs) in quasar spectra and 14 H2 absorption systems along the lines of sight towards stars in the Milky Way and the Magellanic Cloud galaxies. These systems have strong H2 components, with a column density log N(H2)/[cm−2] > 18 and associated C i absorptions. We find that H2-bearing media in high-redshift DLAs and in local galaxies have similar values of the kinetic temperatures Tkin ∼ 100 K and number density 10−500 cm−3. However, the intensity of incident UV radiation in DLAs varies in a wide range (0.1−100 units of the Mathis field), while it is ∼0.1−3 units of the Mathis field for H2 systems in the Milky Way and Large and Small Magellanic Cloud galaxies. The large dispersion of measured UV flux in DLAs is probably a consequence of the fact that the DLA sample probes galaxies selected from the overall galaxy population at high redshift, and therefore corresponds to a wide range of physical conditions.

Radiative cooling dynamics of isolated N2O+ ions in a cryogenic electrostatic ion storage ring

We study radiative cooling processes of ${\mathrm{N}}_{2}{\mathrm{O}}^{+}$ ions isolated in vacuum by taking advantage of the extended storage times possible with a cryogenic electrostatic ion storage ring. The temporal evolution of the internal state populations of the ${\mathrm{N}}_{2}{\mathrm{O}}^{+}$ ions after being stored in the ring was state-selectively measured by action spectroscopy via a predissociation process using a wavelength-tunable pulsed laser. The rotational level population remained unchanged up to about 200 s after ion storage, which is consistent with theoretical predictions and the small permanent dipole moment. On the other hand, we found that depletion of the vibrational excited states in the NN-O stretching mode proceeded within 5 s, while a noticeable increase of the ground-state population was not observed. This implies that the initial populations of the vibrational excited states are relatively small. We discuss such behavior in the context of the initial population distribution of ions extracted from the ion source with a simulation based on simple cascade modeling.

Nature of the DLA towards Q 0528−250: High pressure and strong UV field revealed by excitation of C i, H2, and Si ii

ABSTRACT We present the detection of excited fine-structure energy levels of singly ionized silicon and neutral carbon associated with the proximate damped Lyman-α system at zabs = 2.811 towards Q 0528−250. This absorber has an apparent relative velocity that is inconsistent with the Hubble flow indicating motion along the line-of-sight towards the quasar, i.e. zabs > zem. We measure the metallicity of the system to be [Zn/H] = −0.68 ± 0.02. Using the relative populations of the fine-structure levels of Si ii and C i, as well as the populations of H2 rotational levels, we constrain the physical conditions of the gas. We derive hydrogen number densities of $n_{\rm H}=190^{+70}_{-50}$ cm−3 and $260^{+30}_{-20}$ cm−3 in two velocity components where both C i and H2 are detected. Taking into account the kinetic temperature in each component, ∼150 K, we infer high values of thermal pressure in the cold neutral medium probed by the observations. The strengths of the UV field in Draine’s unit are $I_{\rm UV} = 10^{+5}_{-3}$ and $14^{+3}_{-3}$ in each of these two components, respectively. Such enhanced UV fluxes and thermal pressure compared to intervening DLAs are likely due to the proximity of the quasar. The typical size of the absorber is ∼104 au. Assuming the UV flux is dominated by the quasar, we constrain the distance between the quasar and the absorber to be ∼150−200 kpc. This favours a scenario where the absorption occurs in a companion galaxy located in the group where the quasar-host galaxy resides. This is in line with studies in emission that revealed the presence of several galaxies around the quasar.

Improved Analysis of Ultraviolet Absorption Spectra Under Nonequilibrium Shock Conditions

A landmark set of measurements of high-temperature relaxation under strong shock heating conditions, conducted in 2013 by Ibraguimova et al. (“Investigation of Oxygen Dissociation and Vibrational Relaxation at Temperatures 4000–10800 K,” Journal of Chemical Physics, Vol. 139, No. 3, 2013, Paper 034317) using ultraviolet (UV) absorption converted to time-dependent vibrational temperature profiles, have been receiving considerable attention in the literature as a test of nonequilibrium thermochemical models. A number of attempts by computational fluid dynamics modelers to reproduce the published results were unsuccessful in predicting the peak vibrational temperature, the downstream slope, or both. Our recent analysis has shown that some of the assumptions used in spectra-to-temperature conversions, such as the two-temperature approximation, are violated in the early region of the shock, and a more detailed analysis and direct comparison of UV absorption, and not temperatures, is necessary. This work presents such an analysis where a gas number density, translational temperature, and distribution of rotational and vibrational level populations, obtained using a kinetic gas dynamic approach, are converted into UV in-band absorption for each temporal or spatial location in the shock using a detailed spectroscopic model. The computed UV absorption is then directly compared with the raw measured time-dependent UV absorption curves at several wavelengths. Such a comparison is shown to have more validity than the previous ones.

Dissociation dynamics of carbon dioxide cation (CO2 +) in the C2Σg + state via [1+1] two-photon excitation.

The dissociation dynamics of CO2 + in the C2Σg + state has been studied in the 8.14-8.68 eV region by [1+1] two-photon excitation via vibronically selected intermediate A2Πu and B2Σu + states using a cryogenic ion trap velocity map imaging spectrometer. The cryogenic ion trap produces an internally cold mass selected ion sample of CO2 +. Total translational energy release (TER) and two-dimensional recoiling velocity distributions of fragmented CO+ ions are measured by time-sliced velocity map imaging. High resolution TER spectra allow us to identify and assign three dissociation channels of CO2 + (C2Σg +) in the studied energy region: (1) production of CO+(X2Σ+) + O(3P) by predissociation via spin-orbit coupling with the repulsive 14Πu state; (2) production of CO+(X2Σ+) + O(1D) by predissociation via bending and/or anti-symmetric stretching mediated conical intersection crossing with A2Πu or B2Σu +, where the C2Σg +/A2Πu crossing is considered to be more likely; (3) direct dissociation to CO+(A2Π) + O(3P) on the C2Σg + state surface, which exhibits a competitive intensity above its dissociation limit (8.20 eV). For the first dissociation channel, the fragmented CO+(X2Σ+) ions are found to have widely spread populations of both rotational and vibrational levels, indicating that bending of the parent CO2 + over a broad range is involved upon dissociation, while for the latter two channels, the produced CO+(X2Σ+) and CO+(A2Π) ions have relatively narrow rotational populations. The anisotropy parameters β are also measured for all three channels and are found to be nearly independent of the vibronically selected intermediate states, likely due to complicated intramolecular interactions in the studied energy region.

Laboratory Study of Rate Coefficients for H2:H2 Inelastic Collisions between 295 and 20 K

A laboratory study of state-to-state rate coefficients (STS rates) for H2:H2 inelastic collisions in the v = 0 state is reported. The study, which spans the 295–20 K thermal range, is based on the use of a kinetic master equation. It describes the time-space evolution of populations of H2 rotational levels as induced by inelastic collisions. It is applied here to a supersonic jet of natural H2. This medium bears a large amount of relevant data that allows for the establishment of best values and confidence margins for the dominant STS rates of H2:H2 inelastic collisions on an experimental basis. The primary experimental data derived from the supersonic jet are the local number density, the populations of the H2 rotational levels, and their gradients along the jet by means of high-sensitivity Raman spectroscopy with superb space resolution. First, two sets of theoretical STS rates from the literature have been tested against the experiment. The set that shows a better agreement with the experiment has then been scaled to derive an improved set of experiment-scaled STS rates (ES rates). They allow the reproduction of more than 50 experimental population gradient data within a standard deviation <1.4% along the 295–20 K thermal range. The estimated uncertainty for the ES rates ranges from ≈3% near 300 K to ≈6% near 20 K. ES rates and uncertainties for H2:H2 ground-state inelastic collisions between 300 and 20 K are presented in machine-readable format. Other (incomplete) sets of theoretical rates from the literature are discussed.

Mechanisms for varying non-LTE contributions to OH rotational temperatures from measurements and modelling. II. Kinetic model

OH rotational temperatures Trot deviate from kinetic temperatures Tkin if the rotational level populations derived from the measured OH lines are not in local thermodynamic equilibrium (LTE). In particular,. from OH bands wi Trot th high upper vibrational level appear to be affected by incomplete rotational relaxation and corresponding non-LTE temperature excesses ΔTNLTE. The processes that lead to these non-LTE effects and their variations have not been investigated in detail so far since this requires thorough modelling of the rotational relaxation based on suitable observing data. We performed such an effort for the vibrational level v=9. As it is the highest v that can be populated by the OH-producing hydrogen–ozone reaction, the relaxation processes are the least complex ones. Nevertheless, there are many systematic uncertainties. Therefore, we studied the ΔTNLTE depending on the Einstein A-coefficients used, the very uncertain rate coefficient for the v=9 deactivating collisions of OH with atomic oxygen, and the input profiles for Tkin, air density, and the volume mixing ratios of N2, O2, O, and O3. For the profiles, we used SABER products, where we adapted the O retrieval for a better agreement with the model, and the empirical NRLMSISE-00 model. The profiles were selected or calculated for the Cerro Paranal region in Chile since this allowed us to combine OH Trot measurements based on high-resolution spectra of the UVES spectrograph at the Very Large Telescope with the SABER Tkin and OH emission profiles for an alternative, fully observation-based ΔTNLTE derivation. Moreover, we measured OH(v=9) rotational level populations up to the rotational state N=10 based on UVES OH(9-3) and OH(9-4) line measurements. With these data in comparison with a grid of models, we derived the best-fitting crucial rate coefficients for the rotational relaxation at v=9, which have not been studied before. With the final models, we calculated ΔTNLTE climatologies and compared them with those from the UVES-based data. Significant ΔTNLTE and similar variability structures could be identified. Moreover, we analysed the model in order to find the mechanisms that cause the variations. Here, the steep increase of ΔTNLTE with altitude combined with the height variations of the OH layer appears to be the most important process.

Mechanisms for varying non-LTE contributions to OH rotational temperatures from measurements and modelling. I. Climatology

Rotational temperatures Trot from OH line intensities are an important approach to study the Earth's mesopause region. However, the interpretation can be complicated as the resulting Trot are effective values weighted for the varying OH emission layer. Moreover, the measured Trot only equal kinetic temperatures Tkin if the rotational level population distribution for the considered OH lines is fully thermalised. In many cases, this basic condition of a local thermodynamic equilibrium (LTE) does not seem to be fulfilled. In order to better understand the non-LTE temperature excesses ΔTNLTE and their variations, we used Trot measurements based on 1526 high-resolution spectra of the UVES spectrograph at the Very Large Telescope at Cerro Paranal in Chile in combination with Tkin weighted for the OH emission layer based on 4496 nighttime temperature and OH emission profiles from the SABER radiometer onboard TIMED taken at a similar location. Both data sets were linked via climatologies consisting of the nighttime and seasonal temperature variations. The study focusses on the non-LTE effects at the vibrational level v=9, which is directly populated by the OH-producing hydrogen–ozone reaction and therefore especially prone to incomplete thermalisation of the rotational level population. In comparison to the less critical v=3, the ΔTNLTE climatology showed clear and strongly variable temperature excesses of several kelvins with minima in the evening around the equinoxes and a reliable maximum in the second half of the night around the turn of the year. The Trot non-LTE contributions are positively correlated with the effective OH emission height and volume mixing ratio of atomic oxygen. A significant anti-correlation is found for the air density. Thus, especially variations in the OH emission layer altitude and shape, which are related to changes in the layer-weighted chemical composition and density, are important for the amount of ΔTNLTE.

NH2- in a cold ion trap with He buffer gas: Ab initio quantum modeling of the interaction potential and of state-changing multichannel dynamics.

We present an extensive range of accurate ab initio calculations, which map in detail the spatial electronic potential energy surface that describes the interaction between the molecular anion NH2- (1A1) in its ground electronic state and the He atom. The time-independent close-coupling method is employed to generate the corresponding rotationally inelastic cross sections, and then the state-changing rates over a range of temperatures from 10 to 30 K, which is expected to realistically represent the experimental trapping conditions for this ion in a radio frequency ion trap filled with helium buffer gas. The overall evolutionary kinetics of the rotational level population involving the molecular anion in the cold trap is also modelled during a photodetachment experiment and analyzed using the computed rates. The present results clearly indicate the possibility of selectively detecting differences in behavior between the ortho- and para-anions undergoing photodetachment in the trap.

Rovibrational optical pumping of a molecular beam

Cooling the rotation and the vibration of molecules by broadband light sources was possible for trapped molecular ions or ultracold molecules. Because of a low power spectral density, the cooling timescale has never fell below than a few milliseconds. Here we report on rotational and vibrational cooling of a supersonic beam of barium monofluoride molecules in less than 440 $\mu$s. Vibrational cooling was optimized by enhancing the spectral power density of a semiconductor light source at the underlying molecular transitions allowing us to transfer all the populations of $v''=1-3$ into the vibrational ground state ($v''=0$). Rotational cooling, that requires an efficient vibrational pumping, was then achieved. According to a Boltzmann fit, the rotation temperature was reduced by almost a factor of 10. In this fashion, the population of the lowest rotational levels increased by more than one order of magnitude.

Calculation of the vibration–rotational transition intensities of water molecules trapped in an argon matrix: stretching O–H vibrations spectral region

ABSTRACTThe frequencies and intensities of vibration–rotational transitions of water molecules in an argon matrix were calculated for temperatures of 6 and 30 K. The rigid asymmetric top approximation was used with available literature values of the effective rotational constants in the ground and excited vibrational states. The calculations were carried out by taking into account the existence of a non-equilibrium population distribution between the rotational levels of ortho- and para-water isomers. It was assumed that the temperature relaxation of the population of rotational levels is independent of the ortho- and para-isomers. Comparison of the results of the theoretical calculations with experimental literature data shows good agreement for the majority of the rotational structure lines for symmetric and antisymmetric stretching vibrations both in the frequency values and in the values of the relative intensities.

Spectra, line intensities of the C 1Σ g + ⇒ A 1Σ u + and c 3Σ g + ⇒ a 3Σ u + transitions in liquid normal He, and rotational level populations of the C 1Σ g + and c 3Σ g + the terms

We observed the rotational spectral lines of the He*2 excimer within the range of 910–930 nm in the corona discharge in normal liquid He at the temperature of 4.2 K and the pressure of 1 atm. The spectral range is filled with the rotational lines of the C 1Σ g + ⇒ A 1Σ u + singlet and the c 3Σ g + ⇒ a 3Σ u + triplet transitions. These transitions end at the rotational levels of the lowest metastable terms, A 1Σ u + and a 3Σ u + of the He*2 excimer. Then, the population of the rotational levels with the K' number of the upper C 1Σ g + and c 3Σ g + terms (the quantity of the molecules with the rotational moment of K' in the excited molecule ensemble in the discharge) is proportional to the intensity of the rotational lines marked K' of the C 1Σ g + ⇒ A 1Σ u + singlet and the c 3Σ g + ⇒ a 3Σ u + triplet. The populations might be calculated according to the experimental intensities of the rotational spectral lines. The emitting corona plasma in the liquid He is nonequilibrium and the rotational level populations do not correspond to the Boltzmann distribution. The efficient rotational temperature exceeds the liquid He temperature, 4.2 K.

Comparison of VLT/X-shooter OH and O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; rotational temperatures with consideration of TIMED/SABER emission and temperature profiles

Abstract. Rotational temperatures Trot derived from lines of the same OH band are an important method to study the dynamics and long-term trends in the mesopause region near 87 km. To measure realistic temperatures, the rotational level populations have to be in local thermodynamic equilibrium (LTE). However, this might not be fulfilled, especially at high emission altitudes. In order to quantify possible non-LTE contributions to the OH Trot as a function of the upper vibrational level v′, we studied a sample of 343 echelle spectra taken with the X-shooter spectrograph at the Very Large Telescope at Cerro Paranal in Chile. These data allowed us to analyse 25 OH bands in each spectrum. Moreover, we could measure lines of O2b(0-1), which peaks at about 94 to 95 km, and O2a(0-0) with an emission peak at about 90 km. The latter altitude is reached in the second half of the night after a rise of several km because of the decay of a daytime population of excited O2. Since the radiative lifetimes for the upper levels of the two O2 bands are relatively long, the derived Trot are not significantly affected by non-LTE contributions. These bands are well suited for a comparison with OH if the differences in the emission profiles are corrected. For different sample averages, we made these corrections by using OH emission, O2a(0-0) emission, and CO2-based temperature profile data from the multi-channel radiometer SABER on the TIMED satellite. The procedure relies on differences of profile-weighted SABER temperatures. For an O2a(0-0)-based reference profile at 90 km, we found a good agreement of the O2 with the SABER-related temperatures, whereas the OH temperatures, especially for the high and even v′, showed significant excesses with a maximum of more than 10 K for v′ = 8. The exact value depends on the selected lines and molecular parameters. We could also find a nocturnal trend towards higher non-LTE effects, particularly for high v′. The amplitude of these variations can be about 2 K or less, which tends to be significantly smaller than the total amount of the non-LTE contributions. The variations revealed may be important for dynamical studies based on Trot derived from OH bands with high v′.

Physical conditions in three high-zH2-bearing DLAs: implications for grain size

We present results of our numerical simulation of three H2-bearing damped Lyman alpha absorbers (DLAs) in the redshift interval ~ 2-3. The systems we have modelled are the DLAs at zabs = 2.3377 towards the quasar LBQS 1232+0815, at zabs = 2.41837 towards SDSS J143912.04+111740.5 and at zabs = 2.6265 towards FBQS J081240.6+320808. We have used the spectral synthesis code CLOUDY to simulate the physical environment of these DLAs, and constrain the density, radiation field, geometry and dust-grain properties of the DLAs self-consistently based on the observed column densities of various atomic and molecular species such as H I, fine structure lines of C I and the rotational level population of H2. In our models, we explore the effect of grain size distribution on the predicted column densities of different species. Within the allowed uncertainties in the inferred dust-to-gas ratio, both models with standard ISM grains and smaller-sized grains reproduce the observations equally well. Improved constraints on dust-to-gas ratio and line-of-sight extinction are important for probing the grain size distribution in high-z DLAs. We find the H2-bearing clouds to have line-of-sight thickness in the range 1-6 pc, consistent with what has been found using partial coverage or 21-cm observations in some high-z DLAs.

Computational Study of Competition between Direct Abstraction and Addition-Elimination in the Reaction of Cl Atoms with Propene.

Quasi-classical trajectory calculations on a newly constructed and full-dimensionality potential energy surface (PES) examine the dynamics of the reaction of Cl atoms with propene. The PES is an empirical valence bond (EVB) fit to high-level ab initio energies and incorporates deep potential energy wells for the 1-chloropropyl and 2-chloropropyl radicals, a direct H atom abstraction route to HCl + allyl radical (CH2CHCH2(•)) products (Δ(r)H(298K)(⊖) = −63.1 kJ mol(-1)), and a pathway connecting these regions. In total, 94 000 successful reactive trajectories were used to compute distributions of angular scattering and HCl vibrational and rotational level populations. These measures of the reaction dynamics agree satisfactorily with available experimental data. The dominant reaction pathway is direct abstraction of a hydrogen atom from the methyl group of propene occurring in under 500 fs. Less than 10% of trajectories follow an addition–elimination route via the two isomeric chloropropyl radicals. Large amplitude motions of the Cl about the propene molecular framework couple the addition intermediates to the direct abstraction pathway. The EVB method provides a good description of the complicated PES for the Cl + propene reaction despite fitting to a limited number of ab initio points, with the further advantage that dynamics specific to certain mechanisms can be studied in isolation by switching off coupling terms in the EVB matrix connecting different regions of the PES.