Hydroxyl super rotors from vacuum ultraviolet photodissociation of water

Free electron lasers provide a state-of-the-art tool to investigate the photochemistry of water. Here, the authors show that highly rotationally excited hydroxyl radicals, so-called “super rotors” existing above the bond dissociation energy, are observed from the photodissociation of water, which may have implications for understanding the interstellar medium

VUV Photodissociation Dynamics of Nitrous Oxide: The O(S-1(j=0)) and O(P-3(j=2,1,0)) Product Channels

Vacuum ultraviolet photodissociation dynamics of nitrous oxide was investigated using the time-sliced velocity ion imaging technique. Images of the O(S-1(j=0)) and the O(P-3(j=2,1,0)) products were measured at nine photolysis wavelengths from 124.44 to 133.20 nm, respectively. Three main dissociation channels: O(S-1(0)) + N-2(X-1 Sigma(+)(g)), O(P-3(j=2,1,0)) + N-2(A(3)Sigma(+)(u)), and O(P-3(j=2,1,0)) + N-2(B-3 Pi(g)) were observed and identified in the product images where vibrational states of N2 were fully resolved. Product total kinetic energy releases and angular distributions were acquired. In all product channels, the branching ratios of vibrational states of N-2 products were determined. In addition, the O(P-3(j=2,1,0)) + N-2(A(3)Sigma(+)(u))/O(P-3(j=2,1,0)) + N-2(B-3 Pi(g)) branching ratios were determined. We found that in the O(P-3(j=2,1,0)) channels the O(P-3(j=2,1,0)) + N-2(B-3 Pi(g)) channel becomes dominant at long photolysis wavelength, indicating a strong coupling between the singlet D((1)Sigma(+)(g)) state and the triplet (3)Pi state. For both O(S-1(0)) and O(P-3(j=2,1,0)) products, the derived angular anisotropy parameters (beta values) are very close to 2 at lower vibrational states of the correlated N2 electronic states and gradually decrease with the increasing vibrational quantum number. These behaviors suggest that the photodissociation processes are primarily governed by a fast dissociation in a linear geometry, while the N-2 products at excited vibrational states are very likely produced via a more bent transition state

Vacuum ultraviolet photodissociation dynamics of N2O via the C-1 Pi state: The N(D-2(j=)5/2, (3/2)) + NO(X-2 Pi) product channels

We study the vacuum ultraviolet photodissociation dynamics of N2O via the C-1 Pi state by using the time-sliced velocity map ion imaging technique. Images of N(D-2(j=)5/2, (3/2)) products from the N atom elimination channels were acquired at a set of photolysis wavelengths from 142.55 to 148.19 nm. Vibrational states of the NO(X-2 Pi) co-fragments were partially resolved in experimental images. From these images, the product total kinetic energy release distributions (TKERs), branching ratios of the vibrational states of NO(X-2 Pi) co-fragments, and the vibrational state specific angular anisotropy parameters (beta) have been determined. Notable features were found in the experimental results: the TKERs show that the NO(X-2 Pi) co-fragments are highly vibrationally excited. For the highly vibrationally excited state of NO(X-2 Pi), a bimodal rotational structure is found at all the studied photolysis wavelengths. Furthermore, the vibrational state specific beta values of both spin-orbit channels (j = 3/2, 5/2) clearly show a monotonic decrease as the vibrational quantum number of NO(X-2 Pi) increases. These observations suggest that multiple dissociation pathways play a role in the formation of the N(D-2(j=)5/2, (3/2)) + NO(X-2 Pi) products: one corresponds to a fast dissociation pathway through the linear state (the C-1 Pi state) following the initial excitation to a slightly bent geometry in the vicinity of the linear C-1 Pi configuration, leading to the low rotationally excited components with relatively large beta values; the other corresponds to a relatively slow dissociation pathway through the bent C(3(1)A') or C(3(1)A '') state, leading to moderately rotationally excited NO(X-2 Pi) products with smaller beta values. Published by AIP Publishing

hhdh2d反应的高分辨交叉分子束实验研究

本文利用交叉分子束方法和离子速度成像技术,对H+HD→H2+D反应在1.17 eV碰撞能下的态-态反应动力学开展了高分辨实验研究.实验采用1+1'(真空紫外+紫外)近阈值激光电离方式对反应中的D原子产物进行探测,获得了高角度分辨和高能量分辨的产物离子速度影像,进而精确获得了反应的态-态微分截面.实验观测到了H2(v'=0,j'=1)和H2(v'=0,j'=3)振转产物角分布中与散射过程的干涉效应相联系的前向散射振荡.这一研究进一步表明了化学反应微分截面的精确测量在气相态-态反应动力学研究中的重要性

Photodissociation Dynamics of Nitrous Oxide near 145 nm: The O(S-1(0)) and O(P-3(J=2,1,0)) Product Channels

We report the study of photodissociation dynamics of nitrous oxide in the vacuum ultraviolet region, using the time-sliced velocity map ion imaging technique. Ion images of the O(S-1(0)) and O(P-3(J=2,1,0)) products were measured at nine photolysis wavelengths from 142.55 to 148.79 nm. The product channels O(S-1(0)) + N-2(X-1 Sigma(+)(g)) and O(P-3(J=2,1,0)) + N-2(A(3)Sigma(+)(u)) have been observed. For these dissociation channels, the total kinetic energy releases of the dissociated products were acquired. With vibrational structures of the N-2 coproducts partially resolved in the experimental images, the branching ratios of different vibrational states of the N-2 coproducts were determined, and the vibrational state specific anisotropy parameters (beta values) were derived. Analysis shows that the O(S-1(0)) + N-2(X-1 Sigma(+)(g)) channel is primarily formed via nonadiabatic couplings between the C ((1)Pi) state and the higher-lying D ((1)Sigma(+)) state of the N2O. A moderate rotational excitation and high vibrational excitation of N-2(X-1 Sigma(+)(g)) products have been observed through this pathway. On the other hand, for the O(P-3(J=2,1,0)) + N-2(A(3)Sigma(+)(u)) channels, where a slightly higher rotational excitation of N-2 coproducts have been observed, the possible pathway would be via nonadiabatic couplings from the C ((1)Pi) state to the lower-lying A((1)Sigma(-))state

Observation of the geometric phase effect in the H+HD→H2+D reaction below the conical intersection

The geometric phase effect associated with a conical intersection between the ground and first excited electronic state has been predicted in the H3 system below the conical intersection energy. The authors, by a crossed molecular beam technique and quantum dynamic calculations, provide experimental evidence and insight into its origin

Observation of the Carbon Elimination Channel in Vacuum Ultraviolet Photodissociation of OCS

The textbook mechanism for OCS photodissociation mainly involves the CO + S or CS + O product channel via a single bond fission. However, a third dissociation channel concerning the cleavage of both C-S and C-O bonds yielding SO + C products, though thermodynamically allowed, has never been verified experimentally to date. By using a tunable vacuum ultraviolet laser light and time-sliced velocity map ion imaging technique, we have clearly observed the SO(X-3 Sigma(-)) + C(P-3(j=0)) products as the vacuum ultraviolet laser photon energy gradually exceeds its thermodynamic threshold. The corresponding SO(X-3 Sigma(-)) coproducts are highly vibrationally excited and show varying angular distributions from isotropic to anisotropic as the excitation photon energy increases. Theoretical analysis suggests that a fast nonadiabatic pathway plays a dominant role in the formation of the anisotropic SO products. That isotropic products arise as the excitation photon energies approach the thermodynamic threshold can be reasonably by the "roaming mechanism"