Electron-density contours projected onto the xy, xz, and yz planes for the CH2 molecule in its ground electronic state (left contours) and in its excited electronic state (right contours). The geometry is defined in Fig. 1 of Ref. 1.
(Left-hand panel) The dependence on the bending angle of the energies of the (red curve) and the (blue curve) states of CH2. In both cases the CH2 bond lengths are frozen at their equilibrium values [2.031 bohr (Ref. 11)] for the state and [2.101 bohr (Ref. 12)] for the state. The horizontal lines indicate the positions of the vibrational levels, designated (v a ,v b ,v s ) where the subscripts a, b, and s denote the antisymmetric stretch, the bend, and the symmetric stretch modes, respectively. (Right-hand panel) The dependence of the bending probability (the square of the bending wave function) on the bending angle ρ for the vibrational states (0,0,0) (red) and (0,3,0) (blue). For consistency with the earlier work of Bunker, Hougen, and Johns13 the abscissa ρ is the supplement of the bending angle γ.
Contour plot (cm−1) of the dependence on the orientation of the He atom of the –He (left panel) and –He (right panel) PES’s. In both cases the CH2–He distance is frozen at the value corresponding to the global minimum: R = 6.95 bohrs for the state and R = 4.58 bohrs for the state. Negative contours are indicated in blue, positive in red. The right-hand panel reprinted with permission from L. Ma, M. H. Alexander, and P. J. Dagdigian, J. Chem. Phys.134, 154307 (2011)10.1063/1.3575200. Copyright © 2011, American Institute of Physics.
Dependence of potential energies on ϕ when θ = 90° (motion in the xy plane) for the –He (left) and –He (right) systems.
Dependence of the largest expansion coefficients v λμ on the atom-molecule distance R. Over this range the dominant anisotropic terms are v 31(R) and v 20(R).
Lower rotational levels of the ortho (dashed blue) and para (solid red) nuclear spin modifications of in the (0,0,0) and (0,3,0) vibrational manifolds. Each individual level is labelled , where n is the rotational angular momentum with k a its (nominal) projection along the principal axis and k c , its (nominal) projection along the prolate axis.
Bar plot of the cross sections for rotationally inelastic scattering of the n = 4 and 5, k a =1 levels in the (0,3,0) vibrational manifold of para (left figures) and ortho (right figures) by collision with He at a collision energy of 300 . Red marks the initial state.
Removal cross sections for –He collisions at 300 cm−1 for molecules in different k a = 1 states [para in filled circles (red in color) and ortho in filled squares (blue in color)] in the (0,3,0) vibrational manifold. The largest set of cross sections refers to transitions out of the k a = 1 stack into both the k a = 0 and 1 levels. The two smaller sets of cross sections refer to total removal into, separately, the k a = 0 and k a = 1 stacks.
Bar plot of cross sections for rotationally inelastic scattering from n = 4, k a = 1 levels of the ortho to final levels with n up to 8 in (0,0,0), (0,1,0), and (0,2,0) vibrational states (from top to bottom) by collision with He at a collision energy of 300 cm−1. Red marks the initial level.
Theoretical and experimental (Ref. 10) total removal rate constants for the k a = 1 levels of ortho CH2 by collision with He at room temperature. (Note that experimental results were not obtained for all rotational levels). The points designated by filled circles (red in color), corresponding to relaxation of the state, are from calculations reported in Ref. 1, while the points designated by filled squares (blue in color), corresponding to relaxation of the state, are from the calculations reported here. Also shown (open square, green in color) is the calculated relaxation rate of the n = 9, k a = 3 level of the (0,2,0) manifold. One spin component of this level is mixed with the j = 8, k a = 1 level of the (0,0,0) manifold of the state. The experimentally observed (Ref. 10) relaxation rates of the two mixed levels are shown by the points marked “S” (primarily singlet) and “T” (primarily triplet).
Total removal cross sections out of the n = 4 and 5, k a = 1 levels in the (0,3,0) vibrational state of para and ortho by collision with He at a collision energy of 300 cm−1.
Energy gaps for several Δn transitions out of the n = 4, k a = 1 (413) level of ortho- in the (v s , v b , v a = 0, 0, 0), (0,1,0), (0,2,0), and (0,3,0) vibrational manifolds.a
Overall inelastic cross sections for transitions out of the n = 4, k a = 1 level of ortho and para , and out of the j = 4, k a = 1 level of the (0,0,0) manifold of by collision with He at a collision energy of 300 cm−1.a
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