Nan-Quan Lou

Effect of location of energy barrier on the product alignment of reaction A+BC

The trajectory calculations of heavy heavy–light, light light–light, heavy light–light, and light heavy–light mass combination reactions on attractive and repulsive potential surfaces have been carried out to study the dependence of the product rotational alignment on collision energies. The calculated results for heavy heavy–light mass combination reaction are compared with the predictions from the constrained product orbital angular momentum model. The final rotational angular momentum was found to be perpendicularly polarized with respect to the reagents’ relative velocity vector on either attractive or repulsive potential surface. There is similar behavior of the product rotational alignments as a function of collision energies for heavy heavy–light and heavy light–light reactions, i.e., the more anisotropic the distribution of the product rotational angular momentum vector is, the higher the collision energies are, whether the potential surface is attractive or repulsive. However, the calculations fo...

Rotational alignment of product molecules from the reactions Sr+CH3Br, C2H5Br, n-C3H7Br, i-C3H7Br by means of PLIF

Abstract Rotational alignment of the product SrBr in the beam-gas reactions Sr+RBr (RCH 3 , C 2 H 5 , n -C 3 H 7 , and i -C 3 H 7 was studiedin experiment and theory. The rotational alignment was probed by means of the polarized laser-induced fluorescence (PLIF) of the product. The distributions of the rotational vector become less anisotropic with the increment of the numbers of the carbon atoms in RBr. Moreover, a simple dynamical model was used to calculate the product rotational alignment. The theoretical results are in good agreement with the experimental ones.

Theoretical study of stereodynamics for the reactions Cl+H2/HD/D2

Studies on the dynamical stereochemistry of the Cl+H2 reaction and its isotopic variants, especially the isotope effect on the product polarization, have been performed at a collision energy of 6.0 kcal/mol on two potential energy surfaces, i.e., G3 surface [T. C. Allison et al., J. Phys. Chem. 100, 13575 (1996)] and BW2 surface [W. Bian and H.-J. Werner, J. Chem. Phys. 112, 220 (2000)]. Quantum mechanical and quasiclassical trajectories calculations of the polarization-dependent differential cross sections for the Cl+H2 reaction have been carried out on the BW2 potential energy surface, and the results indicate that the quasiclassical approximation in general does as good as exact quantum mechanics. Calculations also show that the rotational alignment of the HCl product obtained on the BW2 surface for Cl+H2 reaction is stronger than that calculated on the G3 surface, which implies that the effect of van der Waals force on product polarization is quite weak. The distributions of P(θr) and P(φr) derived fr...

Vector correlation in the H+D2 reaction and its isotopic variants: isotope effect on stereodynamics

The vector correlations in the H + D-2 reaction and its isotopic variants at a collision energy of 35.7 kcal/mol have been studied by using quasiclassical trajectories on two potential energy surfaces (PESs), one from BKMP2, and the other from LSTH. And the isotope effect on dynamical stereochemistry is discussed in detail. The calculations indicate that the distribution of the product angular momentum vector is sensitive to the mass factor. The agreement of the results calculated on both the LSTH and BKMP2 PESs probably implies that the product rotational polarization is mainly controlled by the saddle point properties on PES, (C) 2002 Published by Elsevier Science B.V.

Photodissociation of bromobenzene at 266 nm

The photodissociation of C6H5Br at 266 nm has been investigated on the universal crossed molecular beam machine, and time-of-flight spectra as well as the angular distribution of Br atom have been measured. Photofragment translational energy distribution P(Et) reveals that about 47% of the available energy is partitioned into translational energy. The anisotropy parameter β at this wavelength is −0.7±0.2. From P(Et) and β, we deduce that C6H5Br photodissociation is a fast process and the transition dipole moment is almost perpendicular to the C–Br bond. Ab initio calculations have been performed, and the calculated results show that the geometry of the first excited state of bromobenzene has changed apparently compared with that of the ground state. Two kinds of possible fast dissociation mechanism have also been proposed.

Reaction dynamics of the Sr(3RJ) + RI → SrI∗ + R (R = CH3, CH3CH2) systems: rotational alignment, electronic state branching ratio and vibrational state population of products

Abstract The Sr ( 3 P J ) + RI → SrI ( A 2 Π 1 2 , 3 2 ; B 2 Σ + ) + R ( R = CH 3 , CH 3 CH 2 ) reactions have been studied by measuring their chemiluminescence under beam-gas conditions. The rotational alignment of the product SrI was obtained. In addition, the electronic state branching ratio and the product vibrational state population have been roughly estimated by simulating the chemiluminescent spectra of SrI.

Photodissociation of chlorobenzene at 266 nm

Abstract The photodissociation of C 6 H 5 Cl at 266 nm has been investigated using the crossed laser–molecular beam technique. The translational energy distribution of the Cl photofragment is obtained. The TOF spectrum of the Cl fragment consists of only one component. Ab initio calculation shows that the first excited state of chlorobenzene has large geometry changes compared to that of the ground state. The hot molecule mechanism is considered to be probable for the dissociation of C 6 H 5 Cl at 266 nm.

A real time dynamical calculation of H2− photodissociation

Abstract A one-dimensional wavepacket study of a two-state system (H2−), coupled by a laser pulse, is presented. The wavepacket time evolution on a repulsive excited potential surface is simulated for a weak laser field as well as for a strong one. The complex lifetime of H2− photodissociation is calculated to be about 8.5 fs. The deformation of the ground state wavepacket under a strong laser field has been discussed and it is found that the strong field did not only induce the electronic state excitation but also resulted in the vibrational excitation of the electronic ground state in H2− photodissociation.

Comparison of the dynamics of the reactions of Ba with aromatic halides and alkyl halides. LIF studies of the reactions of Ba with C6H5X (X=Cl, Br, I)

Abstract Nascent internal state energy distributions of BaX have been studied for the reactions Ba + C 6 H 5 X→BaX+C 6 H 5 (X  Cl, Br, 1) using the laser-induced fluorescence method in a beam-gas arrangement. The energy disposal differs markedly from that of the reactions Ba + CH 3 X. With the change of X from Cl to I, the vibrational excitations and the reactive cross sections decrease for the reactions Ba + C 6 H 5 X, whereas those of the reactions Ba + CH 3 X increase. The CNDO/2 calculations of C 6 H 5 X and CH 3 X have been used to interpret the experimental results qualitatively.

Comparison of the dynamics of the reactions of Ca ground and metastable atoms with CH2Cl2 and CHCl3

Abstract Laser-induced fluorescence (LIF) is used to study the reactions of Ca( 1 S 0 ) and Ca( 3 P) with CH 2 Cl 2 and CHCl 3 . The internal energy distributions of the ground state CaCl reaction products are reported.