Time-sliced Velocity Map Ion Imaging Research Articles

Photodissociation dynamics of SO2 via the G̃1B1 state: The O(1D2) and O(1S0) product channels.

Produced by both nature and human activities, sulfur dioxide (SO2) is an important species in the earth's atmosphere. SO2 has also been found in the atmospheres of other planets and satellites in the solar system. The photoabsorption cross sections and photodissociation of SO2 have been studied for several decades. In this paper, we reported the experimental results for photodissociation dynamics of SO2 via the G̃1B1 state. By analyzing the images from the time-sliced velocity map ion imaging method, the vibrational state population distributions and anisotropy parameters were obtained for the O(1D2) + SO(X3Σ-, a1Δ, b1Σ+) and O(1S0) + SO(X3Σ-) channels, and the branching ratios for the channels O(1D2) + SO(X3Σ-), O(1D2) + SO(a1Δ), and O(1D2) + SO(b1Σ+) were determined to be ∼0.3, ∼0.6, and ∼0.1, respectively. The SO products were dominant in electronically and rovibrationally excited states, which may have yet unrecognized roles in the upper planetary atmosphere.

Wavelength-Dependent Dynamics of the O(1D2) Channel in the 1Δu State Photodissociation of CO2.

The wavelength-dependent dynamics of the O(1D2) channel, formed by photoexcitation of CO2 to the 1Δu state at 143.53-153.03 nm, is investigated by using the time-sliced velocity-mapped ion imaging method. The measured ionic peaks of the O(1D2) images are analyzed to determine the total kinetic energy release (TKER) spectra and image anisotropy parameters. The structures observed in the TKER spectra can be directly assigned to the ro-vibrational state distributions of the counter CO photofragments. Compared to those observed at 157 and 155 nm, the highly rotationally excited CO photofragments still obviously appear in v = 0 and 1, but the fraction of rotational excitations is significantly reduced. Conversely, the CO photofragments exhibit substantially higher vibrational excitations, implying that the nearly linear 21A' state also contributes to dissociation in addition to the bend configuration. The image anisotropy parameters display an extremely slow decreasing trend with an increase of the CO ro-vibrational state besides those for the highest ro-vibrationally excited CO photofragments. Nevertheless, the nonaxial recoil effect, suggested in previous photodissociation studies of CO2 and other triatomic molecular systems, is still appropriate to explain the observations of internal energy dependences of image anisotropy parameters.

Photodissociation of CO2 via the 1Πg state: Wavelength-dependent imaging studies of O(1D2) photoproducts.

Photodissociation of CO2 via the 1Πg state is investigated using a time-sliced velocity-mapped ion imaging apparatus combined with a tunable vacuum ultraviolet photolysis source. The main O(1D2) + CO(X1Σ+) channel is directly observed from the measured images of O(1D2) photoproducts at 129.08-134.76nm. The total kinetic energy release spectra determined based on these images show that the energetic thresholds for the O(1D2) + CO(X1Σ+) photoproducts correspond to the thermochemical thresholds for the photodissociation of CO2(v2 = 0) and CO2(v2 = 1). One significant difference among the CO(X1Σ+, v) vibrational distributions for the predominant CO2(v2 = 0) dissociation is that the population of CO(v = 0) becomes favorable at 130.23-133.45nm compared to the Boltzmann-like component (v > 0) that always exists at 129.08-134.76nm. The wavelength dependences of the overall β are found to follow the variation trend of the CO(v = 0) abnormal intensity. The vibrational state-specific β values present a roughly decreasing trend with an increase in v, whereas β(v = 0) appears to be significantly larger than β(v = 1) at 130.23-133.45nm compared to 134.76 and 129.08nm. The non-statistical CO(v = 0) with larger β values at 130.23-133.45nm implies that an additional pathway may open through the conical intersection coupling to the dissociative 21A' state, except for the ever-existing pathway that yields the Boltzmann-like component. In contrast, at 129.08nm, the restoration of the statistical equilibrium in the CO(X1Σ+, v) vibrational distribution may be caused by the emergence of novel dissociation pathways arising from the participation of the 31A″ state.

Photodissociation dynamics of SO2 between 193 and 201 nm.

The nonadiabatic interactions between the C̃ state and neighboring electronic states of SO2 have attracted much attention; however, the predissociation mechanisms are not yet completely understood. In this work, the predissociation dynamics of SO2 via its C̃ state have been investigated at λ = 193-201nm by using the time-sliced velocity map ion imaging technique. The translational energy distributions and the branching ratios of the O(3PJ=2,1,0) spin-orbit products at six photolysis wavelengths have been acquired. The SO(3Σ-) product population gradually decreases in v = 0 and increases in v = 2 as the photolysis wavelength decreases. The branching ratios of O(3P J=2,1,0) products are almost similar at most wavelengths, except at 194.8nm. Our data suggest that the predissociation between 193 and 201nm is via an avoided crossing between the C̃ state and the repulsive triplet 23A' state. The state-to-state dynamical pictures shown in this work provide a rigorous test of the potential energy surfaces (PESs) of the SO2 and the nonadiabatic couplings between these PESs.

Photodissociation dynamics of H2S+ near 325 nm

We study the photodissociation dynamics of the hydrogen sulfide cations (H2S+) using the time-sliced velocity map ion imaging (VMI) technique and high-accuracy calculations. High-resolution ion images of the S+(4S) products were measured at four photolysis wavelengths of 325.158, 325.200, 325.243, 325.307 nm, which correspond to the excitation to the A2A1(0,13,0) K=1 state of H2S+. Rotational state-resolved total kinetic energy releases and angular distributions have been derived as a function of the photolysis wavelengths. Notably, photolysis wavelength dependent product rotational state and anisotropy parameter distributions have been clearly observed. Full-dimensional potential energy surface characterization suggests that nonadiabatic coupling between A2A1 and B2B2 states at C2v configurations, as well as relaxation of the symmetry to Cs in the conical intersection region between the two states, plays a key role in the photodissociation process.

Resonance-state selective photodissociation dynamics of OCS + hv → CS(X1Σ+) + O(3Pj=2,1,0) via the 21Σ+ state.

Understanding vacuum ultraviolet photodissociation dynamics of Carbonyl sulfide (OCS) is of considerable importance in the study of atmospheric chemistry. Yet, photodissociation dynamics of the CS(X1Σ+) + O(3Pj=2,1,0) channels following excitation to the 21Σ+(ν1',1,0) state has not been clearly understood so far. Here, we investigate the O(3Pj=2,1,0) elimination dissociation processes in the resonance-state selective photodissociation of OCS between 147.24 and 156.48nm by using the time-sliced velocity-mapped ion imaging technique. The total kinetic energy release spectra are found to exhibit highly structured profiles, indicative of the formation of a broad range of vibrational states of CS(1Σ+). The fitted CS(1Σ+) vibrational state distributions differ for the three 3Pj spin-orbit states, but a general trend of the inverted characteristics is observed. Additionally, the wavelength-dependent behaviors are also observed in the vibrational populations for CS(1Σ+, v). The CS(X1Σ+, v = 0) has a significantly strong population at several shorter wavelengths, and the most populated CS(X1Σ+, v) is gradually transferred to a higher vibrational state with the decrease in the photolysis wavelength. The measured overall β-values for the three 3Pj spin-orbit channels slightly increase and then abruptly decrease as the photolysis wavelength increases, while the vibrational dependences of β-values show an irregularly decreasing trend with increasing CS(1Σ+) vibrational excitation at all studied photolysis wavelengths. The comparison of the experimental observations for this titled channel and the S(3Pj) channel reveals that two different intersystem crossing mechanisms may be involved in the formation of the CS(X1Σ+) + O(3Pj=2,1,0) photoproducts via the 21Σ+ state.

Photodissociation study of CO2 on the formation of state-correlated CO(X1Σ+, v) with O(3P2) photoproducts in the low energy band centered at 148 nm.

The spin-forbidden O(3P2) + CO(X1Σ+, v) channel formed from the photodissociation of CO2 in the low energy band centered at 148nm is investigated by using the time-sliced velocity-mapped ion imaging technique. The vibrational-resolved images of the O(3P2) photoproducts measured in the photolysis wavelength range of 144.62-150.45nm are analyzed to give the total kinetic energy releases (TKER) spectra, CO(X1Σ+) vibrational state distributions, and anisotropy parameters (β). The TKER spectra reveal the formation of correlated CO(X1Σ+) with well resolved v = 0-10 (or 11) vibrational bands. Several high vibrational bands that were observed in the low TKER region for each studied photolysis wavelength exhibit a bimodal structure. The CO(X1Σ+, v) vibrational distributions all present inverted characteristics, and the most populated vibrational state changes from a low vibrational state to a relatively higher vibrational state with a change in the photolysis wavelength from 150.45 to 144.62nm. However, the vibrational-state specific β-values for different photolysis wavelengths present a similar variation trend. The measured β-values show a significant bulge at the higher vibrational levels, in addition to the overall slow decreasing trend. The observed bimodal structures with mutational β-values for the high vibrational excited state CO(1Σ+) photoproducts suggest the existence of more than one nonadiabatic pathway with different anisotropies in the formation of O(3P2) + CO(X1Σ+, v) photoproducts across the low energy band.

Fine-structure branching ratios N(2D5/2)/N(2D3/2) above threshold N(2D5/2.3/2)+N(2D5/2.3/2) for 14N2 and 15N2

Accurate measurements of the product spin-orbit finne-structure branching ratios are important for understanding the detailed photodissociation dynamics of small molecules. In this study, the atomic spin-orbit fine-structure branching rar tio N(2D5/2)/N(2D3/2) to the dissociation channel N(2D5/2,3/2)+N(2D5/2,3/2) is measured for the c4′1Σu+(υ′=6) and b′1Σu+(υ′=21) states of 14N2, and the b′1Σu+(υ′=20) and b′1Σu+(υ′=21) states of 15N2 by using the vacuum ultraviolet (VUV)pump VUV-probe time-sliced velocity-mapped ion imaging setup. The measurements show that the fine-structure branching ratio N(2D5/2)/N(2D3/2) is independent of the rotational level of the parent molecule (14N2 or 15N2) in each vibronic state, while it does show dependence on the vibronic characteristics. It is ~1.35 for the c4′1Σu+(υ′=6) state of 14N2 and b′1Σu+(υ′=20) state of 15N2, which are both close to the dissociation threshold N(2D5/2,3/2)+N(2D5/2,3/2); while it becomes ~1.00 for the b′1Σu+(υ′=21) state of both 14N2 and 15N2, which are relatively far above the dissociation threshold. A possible change from a statistical process near the threshold to a diabatic process far above the threshold might have occurred to be responsible for the observed vibronic dependence of the branching ratio. Detailed informations on the potential energy curves and their mutual couplings near the dissociation threshold are highly desired for understanding the present experimental measurement.

Slice imaging study of NO2 photodissociation via the 12B2 and 22B2 states: the NO(X2Π) + O(3PJ) product channel.

The state-resolved photodissociation of NO2via the 12B2 and 22B2 excited states has been investigated by using time-sliced velocity-mapped ion imaging technique. The images of the O(3PJ=2,1,0) products at a series of excitation wavelengths are measured by employing a 1 + 1' photoionization scheme. The total kinetic energy release (TKER) spectra, NO vibrational state distributions and anisotropy parameters (β) are derived from the O(3PJ=2,1,0) images. For the 12B2 state photodissociation of NO2, the TKER spectra mainly present a non-statistical vibrational state distribution of the NO co-products, and the profiles of most vibrational peaks display a bimodal structure. The β values show a gradual decrease with the photolysis wavelength increasing except for a sudden increase at 357.38 nm. The results suggest that the NO2 photodissociation via the 12B2 state proceeds via the non-adiabatic transition between the 12B2 and X̃2A1 states, leading to the NO(X2Π) + O(3PJ) products with wavelength-dependent rovibrational distributions. As for photodissociation of NO2via the 22B2 state, the NO vibrational state distribution is relatively narrow with the main peak shifting from v = 1, 2 at 235.43-249.22 nm to v = 6 at 212.56 nm. The β values exhibit two distinctly different angular distributions, i.e., near isotropic at 249.22 and 246.09 nm and anisotropic at the rest of the excitation wavelengths. These results are consistent with the fact that the 22B2 state potential energy surface has a barrier, and the dissociation process is fast when the initial populated level is above this barrier. A bimodal vibrational state distribution is clearly observed at 212.56 nm, in which the main distribution (peaking at v = 6) is ascribed to dissociation via an avoided crossing with the higher electronically excited state while the subsidiary distribution (peaking at v = 11) likely arises due to dissociation via the internal conversion to the 12B2 state or to the X̃ ground state.

Observation of rotationally dependent fine-structure branching ratios near the predissociation threshold N(2D5/2,3/2) + N(2D5/2,3/2) of 14N2.

Photofragment spin-orbit fine-structure branching ratios have long been predicted to depend on the rotational quantum number J' by theory near the dissociation thresholds of several diatomic molecules, while this has rarely been observed in any photodissociation experiments yet. Here, we measured the fine-structure branching ratios N(2D5/2)/N(2D3/2) produced in the N(2D5/2,3/2) + N(2D5/2,3/2) channel at the b'1Σu +(v = 20) state of 14N2 by using our vacuum ultraviolet (VUV)-pump-VUV-probe time-sliced velocity-mapped ion imaging setup. It is found that 14N2 almost exclusively dissociates into the spin-orbit channel N(2D5/2) + N(2D3/2) at low rotational levels and gradually approaches the statistical or diabatic limit by distributing all possible spin-orbit channels at higher rotational levels. The strongly rotationally dependent fine-structure branching ratios should be due to the increasing strength of nonadiabatic Coriolis interaction among various dissociative states in the so-called "recoupling zone" as J' increases. They are supposed to provide unprecedented information on the near threshold photodissociation dynamics of 14N2.

Photodissociation dynamics of CO2 + hv → CO(X1Σ+) + O(1D2) via the 3P1Πu state.

The vacuum ultraviolet (VUV) photodissociation of CO2 is important to understand the primary photochemical processes of CO2 induced by solar VUV excitation in the Earth's atmosphere. Here, we report a detailed study of vibrational-state-specific photodissociation dynamics of the CO(X1Σ+) + O(1D2) channel via the 3P1Πu state by using the time-sliced velocity-mapped ion imaging apparatus combined with the single VUV photoionization detection scheme. By recording the sliced images of the O(1D2) photoproducts formed by VUV photoexcitation of CO2 to the individual vibrational structure of the 3P1Πu state, both the vibrational state distributions of the counterpart CO(X1Σ+) photoproducts and the vibrational-state-specific product anisotropy parameters (β) are determined. The experimental results show that photodissociation of CO2 at 108.22, 107.50, 106.10, and 104.76nm yields less anisotropic (β > 0) and inverted distributed CO(X1Σ+, v) photoproducts. The possible dissociation mechanism for the CO(X1Σ+) + O(1D2) channel may involve the non-adiabatic transition of excited CO2* from the initially prepared state to the 31A' state with potential energy barriers. While at 108.82 and 107.35nm, the vibrational distributions are found to have the population peaked at a low vibrational state, and the anisotropy parameters turn out to be negative. Such variation indicates the possibility of another non-adiabatic dissociation pathway that may involve Coriolis-type coupling to the low-lying dissociative state. These observations show sclear evidence of the influence of the initially vibrational excitations on the photodissociation dynamics of CO2 via the 3P1Πu state.

Vacuum ultraviolet photodissociation dynamics of OCS via the F Rydberg state: The S(3PJ = 2, 1, 0) product channels

Vacuum ultraviolet (VUV) photodissociation dynamics of carbonyl sulfide was investigated experimentally by using a tunable photolysis light source and the time-sliced velocity map ion imaging technique. Ion images of S(3PJ =2, 1, 0) dissociation products were measured at five photolysis wavelengths from 133.26 nm to 139.96 nm, corresponding to the F Rydberg state of OCS. Two dissociation channels: S(3PJ)+CO(X1Σ+) and S(3PJ)+CO(A3Π) were observed with the former being dominant. The vibrational states of CO co-products were partially resolved in the ion images. The product total kinetic energy releases, anisotropy parameters (β), and the branching ratios of high-lying CO vibrational states were determined for the S(3PJ )+CO(X1Σ+) channel. We found that the anisotropy parameters suddenly changed from negative to positive when OCS was excited to the higher vibrational levels of the F state. Furthermore, the anisotropy parameters for S(3PJ) products of J = 2, 1, 0 were even different. These anomalous phenomena may result from the simultaneous existence of both parallel and perpendicular dissociation mechanisms, suggesting the involvement of other electronic states with different symmetry in the initially-excited energy region. This work provides a further understanding of the nonadiabatic couplings in the VUV photodissociation process of OCS.

Photodissociation dynamics of CS2 near 204 nm: The S(3PJ)+CS(X1Σ+) channels

We study the photodissociation dynamics of CS2 in the ultraviolet region using the time-sliced velocity map ion imaging technique. The S(3PJ)+CS(X1Σ+) product channels were observed and identified at four wavelengths of 201.36, 203.10, 204.85 and 206.61 nm. In the measured images of S(3PJ=2,1,0), the vibrational states of the CS(X1Σ+) co-products were partially resolved and the vibrational state distributions were determined. Moreover, the product total kinetic energy releases and the anisotropic parameters were derived. The relatively small anisotropic parameter values indicate that the S(3PJ=2,1,0)+CS(X1Σ+) channels are very likely formed via the indirect predissociation process of CS2. The study of the S(3PJ=2,1,0)+CS(X1Σ+) channels, which come from the spin-orbit coupling dissociation process of CS2, shows that nonadiabatic process plays a role in the ultraviolet photodissociation of CS2.

Vacuum ultraviolet photodissociation dynamics of N2O+hv→N2(X1Σg+)+O(1S) in the short wavelength tail of D1Σ+ band

Vacuum ultraviolet photodissociation dynamics of N2O+hv→N2(X1Σg+)+O(1S0) in the short wavelength tail of D1Σ+ band has been investigated using the time-sliced velocity-mapped ion imaging technique by probing the images of the O(1S0) photoproducts at a set of photolysis wavelengths including 121.47 nm, 122.17 nm, 123.25 nm and 123.95 nm. The product total kinetic energy release distributions, vibrational state distributions of the N2(X1Σg+) photofragments and angular anisotropy parameters have been obtained by analyzing the raw O(1S0) images. It is noted that additional vibrationally excited photoproducts (3≤v≤8) with a Boltzmann-like feature start to appear except the non-statistical component as the photolysis wavelength decreases to 123.25 nm, and the corresponding populations become more pronounced with decreasing of the photolysis wave-length. Furthermore, the vibrational state specific anisotropy parameter β at each photolysis wavelength exhibits a drastic fluctuation near β=1.75 at v<8, and decreases to a minimum as the vibrational quantum number further increases. While the overall anisotropy parameter β for the N2(X1Σg+)+O(1S0) channel presents a roughly monotonical increase from 1.63 at 121.47 nm to 1.95 at 123.95 nm. The experimental observations suggest that there is at least one fast nonadiabatic pathway from initially prepared D1Σ+ state to the dissociative state with bent geometry dominating to generate the additional vibrational structures at high photoexcitation energies.

Wavelength dependent photodissociation of OCS via F 31Π Rydberg state: CO(X1Σ+)+S(1D2) product channel

The vacuum ultraviolet photodissociation of OCS via the F 31Π Rydberg states was investigated in the range of 134–140 nm by means of the time-sliced velocity map ion imaging technique. The images of S(1D2) products from the CO(X1Σ+)+S(1D2) dissociation channel were acquired at five photolysis wavelengths, corresponding to a series of symmetric stretching vibrational excitations in OCS(F 31Π, υ1=0–4). The total translational energy distributions, vibrational populations and angular distributions of CO(X1Σ+, υ) coproducts were derived. The analysis of experimental results suggests that the excited OCS molecules dissociate to CO(X1Σ+) and S(1D2) products via non-adiabatic couplings between the upper F 31Π states and the lower-lying states both in the C∞υ and Cs symmetry. Furthermore, strong wavelength dependent behavior has been observed: the greatly distinct vibrational populations and angular distributions of CO(X1Σ+, υ) products from the lower (υ1=0–2) and higher (υ1=3, 4) vibrational states of the excited OCS(F 31Π, υ1) demonstrate that very different mechanisms are involved in the dissociation processes. This study provides evidence for the possible contribution of vibronic coupling and the crucial role of vibronic coupling on the vacuum ultraviolet photodissociation dynamics.

Velocity map imaging studies of the photodissociation of CS2 by two-photon excitation at around 303–315 nm

ABSTRACT Two-photon dissociation dynamics of carbon disulfide (CS2) have been studied by using the time-sliced velocity map ion imaging technique. Images of the S (1D2) and S (3P0) photoproducts formed in the CS2 photodissociation are acquired at four photolysis wavelengths from 303 nm to 315 nm. Vibrational states of the CS co-products are partially resolved and identified in the images. The CS (X1Σ+) products are highly vibrationally excited with moderate rotational excitation. The spin–orbit state-specific dissociation dynamics are also investigated by measuring the images of three S (3PJ) spin–orbit states (J=0, 1, and 2) at photolysis wavelength 303.878 nm. The branching ratios of CS (a3Φ)/CS (X1Σg +) are determined to be 0.05 ± 0.02, 0.17 ± 0.04, and 0.26 ± 0.05 for the three spin–orbit states S (3P0), S (3P1), and S (3P2) respectively, implying a strong spin–orbit coupling exists in the dissociation process. The averaged anisotropy parameters β 2>0 and β 4∼0 suggest that the CS2 molecules undergo a sequential transition 21 B 2(21Σ+)←11 B 2(1Δu)←X 1Σg + with the intermediate state 11 B 2 having a long lifetime, followed by nonadiabatic and spin–orbit couplings to other electronic states and then dissociate.

Photodissociation Dynamics of OCS near 150 nm: The S(1SJ=0) and S(3PJ=2,1,0) Product Channels.

Vacuum ultraviolet photodissociation dynamics of carbonyl sulfide (OCS) was investigated by using the time-sliced velocity map ion imaging technique. Images of the S(1SJ=0) and S(3PJ=2,1,0) photofragments formed in the OCS photodissociation were acquired at six photolysis wavelengths from 147.24 to 156.48 nm. Vibrational states of the CO coproducts were partially resolved and identified in the images. Two main dissociation product channels, namely, the spin-allowed S(1SJ=0) + CO(X1Σg+) and spin-forbidden S(3PJ=2,1,0) + CO(X1Σg+), were observed. At each photolysis wavelength, the total kinetic energy releases, the relative population of different CO vibrational states, and the anisotropic parameters were derived. Variations of the relative population were noticed between different spin-orbit states of the S(3PJ) channel. It was found that the S(1SJ=0) + CO(X1Σg+) channel is dominated by the 1Σ+ ← 1Σ+ parallel transition of OCS. Interestingly, two types of anisotropic parameters are found at different photolysis wavelengths for the spin-forbidden S(3PJ=2,1,0) + CO(X1Σg+) product channel. The anisotropic parameters at 147.24 and 150.70 nm are significantly smaller than at the other four photolysis wavelengths. This phenomenon indicates two different nonadiabatic pathways are responsible for the spin-forbidden channels, which is consistent with the barrier structure in the exit channel of one of the triplet states.

Photodissociation dynamics of OCS near 128 nm: S(3PJ=2,1,0), S(1D2) and S(1S0) channels

Here we report the study of the photodissociation dynamics of carbonyl sulfide in the vacuum ultraviolet region using the time-sliced velocity map ion imaging technique. Images of S(3PJ=2,1,0), S(1D2) and S(1S0) products were measured at four photolysis wave-lengths of 129.32, 128.14, 126.99, and 126.08 nm, respectively. Four main dissociation channels: S(3PJ=2,1,0)+CO(X1Σ+), S(3PJ=2,1,0)+CO(A3Π), S(1D2)+CO(X1Σ+) and S(1S0)+CO(X1Σ+) channels, have been clearly observed and identified. Vibrational states of the CO co-products were partially resolved in the experimental images. From these images, the product total kinetic energy releases, the branching ratios and angular distributions of products have been derived. While the S(3PJ=2,1,0)+CO(A3Π) product channel is formed through the adiabatic dissociation process after the excitation to the (31Σ+) excited state, the results suggest that strong nonadiabatic coupling plays an important role in the formation of other three channels.

Imaging reaction dynamics of Y+SO2

The reaction dynamics of yttrium atoms with sulfur dioxide molecules at a high collision energy of 36 kcal/mol was studied using time-sliced velocity map ion imaging, crossed molecular beam and laser-ablation method. The product YO was detected via multiphoton ionization at various wavelengths in the region of 482–615 nm. The slice images of YO show a broad velocity distribution and forward-backward peaking angular distribution. The forward scattering signal is stronger than its backward distribution. This indicates that the reaction proceeds via an intermediate complex and the lifetime of the intermediate state is less than one rotational period. The formation of complex suggests that electron transfer occurs in the oxidation reaction.

Imaging the State-to-State Dynamics of the H + D2 → HD + D Reaction at 1.42 eV.

High-resolution state-resolved differential cross sections (DCSs) are of great importance in understanding quantum reaction dynamics, and they are the most detailed observables that can be experimentally measured. Here we report a synergic crossed molecular beam and quantum reaction dynamics study on the H + D2 reaction. With the time-sliced velocity map ion imaging (VMI) technique and the near-threshold ionization scheme, we acquired the product rovibrational state-resolved DCSs of the H + D2 (v = 0, j = 0) → HD (v', j') + D reaction at a collision energy of 1.42 eV. For HD products with small j' quantum numbers, significant forward scattering with clear angular oscillations was observed. The forward scattering disappears for the rotational states with large j' quantum numbers. Interestingly, as the j' number increases, the peak of the DCS shifts from backward to sideways systematically. The experimental observation agrees very well with theoretical quantum mechanical dynamics results, which reveals that the systematic shift of the peak in the DCS from backward scattering to sideways scattering can be understood very well with the strong correlation between the product rotational quantum number j' and the specific partial waves (J = 3-12), whereas the forward angular oscillations are from the coherent summation of larger partial waves.