Publisher's Note: “Theoretical investigation of rotationally inelastic collisions of CH2(<i>ã</i>) with helium” [J. Chem. Phys. 134, 154307 (2011)]

Quasi-classical trajectory (QCT) methods are presented which allow characterization of the angular momentum depolarization of the products of inelastic and reactive scattering. The particular emphasis of the theory is on three-vector correlations, and on the connection with the two-vector correlation between the initial and final angular momenta, j and j', which is amenable to experimental measurement. The formal classical theory is presented, and computational results for NO(A) + He are used to illustrate the type of mechanistic information provided by analysis of the two- and three-vector correlations. The classical j-j' two-vector correlation results are compared with quantum mechanical calculations, and are shown to be in good agreement. The data for NO(A) + He support previous conclusions [M. Brouard, H. Chadwick, Y.-P. Chang, R. Cireasa, C. J. Eyles, A. O. L. Via, N. Screen, F. J. Aoiz, and J. Kłos, J. Chem. Phys. 131, 104307 (2009)] that this system is only weakly depolarizing. Furthermore, it is shown that the projection of j along the kinematic apse is nearly conserved for this system under thermal collision energy conditions.

Section: Introductionmentioning

confidence: 86%

The k-j-j′ vector correlation in inelastic and reactive scattering

Brouard

Chadwick

Eyles

et al. 2011

“…However, several authors pointed out that infrared transition among the molecular vibrational levels could significantly increase the intensities of the rotational transitions by populating the upper rotational levels [5]. The question of the validity of this approximation was then recently investigated by the group of Alexander and Dagdigian for CH 2 [6]. They calculated the bending levels of CH 2 and averaged the He-CH 2 potential over the bending angle using these functions in order to reduce the problem to a fictitious atomrigid asymmetric top molecule collision.…”

Section: Introductionmentioning

confidence: 99%

Ro-vibrational relaxation of HCN in collisions with He: Rigid bender treatment of the bending-rotation interaction

Stoecklin

Denis-Alpizar

Halvick

et al. 2013

We present a new theoretical method to treat atom-rigid bender inelastic collisions at the Close Coupling (RB-CC) level in the space fixed frame. The coupling between rotation and bending is treated exactly within the rigid bender approximation and we obtain the cross section for the rotational transition between levels belonging to different bending levels. The results of this approach are compared with those obtained when using the rigid bender averaged approximation (RBAA) introduced in our previous work dedicated to this system. We discuss the validity of this approximation and of the previous studies based on rigid linear HCN. We find that l-type transitions cross sections have to be calculated at the RB-CC level for the He-HCN collision while pure rotational transitions cross sections may be calculated accurately at the RBAA level.

“…1. This choice is the same as adopted by Hutson in his theoretical study of Ar + H 2 O collisions 41 but differs from the recent work of Dagdigian and co-workers, where the principal axis of the triatomic is used to define the z axis 29,30 . The CH 2 molecule lies in the xz plane, with the z-axis bisecting the HCH angle, and the y-axis perpendicular to the molecular plane.…”

Section: A Hamiltonianmentioning

confidence: 99%

“…Many authors employed Green's formalism to carry out accurate scattering calculations of rotational cooling rates for interstellar molecules colliding with atomic and molecular species based on accurate ab initio interaction potentials 28 . Several theoretical studies have used a combination of highlevel ab initio and quantum scattering calculations to explore the dynamics of collisioninduced rovibrational relaxation of methylene (CH 2 (a, X)) and methyl (CH 3 ) radicals in room-temperature He buffer gas 29,31 , for which accurate rate measurements have recently become available 32 .…”

Section: Introductionmentioning

confidence: 99%

Cold collisions of polyatomic molecular radicals with S-state atoms in a magnetic field: An ab initio study of He + ${\rm CH}_2(\tilde{X})$ CH 2(X̃) collisions

Tscherbul

Grinev

et al. 2012

Self Cite

We develop a rigorous quantum mechanical theory for collisions of polyatomic molecular radicals with S-state atoms in the presence of an external magnetic field. The theory is based on a fully uncoupled space-fixed basis set representation of the multichannel scattering wave function. Explicit expressions are presented for the matrix elements of the scattering Hamiltonian for spin-1/2 and spin-1 polyatomic molecular radicals interacting with structureless targets. The theory is applied to calculate the cross sections and thermal rate constants for spin relaxation in low-temperature collisions of the prototypical organic molecule methylene [CH(2)(X(3)B(1))] with He atoms. To this end, two accurate three-dimensional potential energy surfaces (PESs) of the He-CH(2)(X(3)B(1)) complex are developed using the state-of-the-art coupled-cluster method including single and double excitations along with a perturbative correction for triple excitations and large basis sets. Both PESs exhibit shallow minima and are weakly anisotropic. Our calculations show that spin relaxation in collisions of CH(2), CHD, and CD(2) molecules with He atoms occurs at a much slower rate than elastic scattering over a large range of temperatures (1 μK-1 K) and magnetic fields (0.01-1 T), suggesting excellent prospects for cryogenic helium buffer-gas cooling of ground-state ortho-CH(2)(X(3)B(1)) molecules in a magnetic trap. Furthermore, we find that ortho-CH(2) undergoes collision-induced spin relaxation much more slowly than para-CH(2), which indicates that magnetic trapping can be used to separate nuclear spin isomers of open-shell polyatomic molecules.