A circularly polarized infrared (IR) laser pulse which propagates along the axis of a pre-aligned linear polyatomic molecule may excite unidirectional pseudorotations corresponding to excitation of the molecular bend and rotation of the bent molecule around that axis. This preparation and spinning a molecular top is, in part, analogous to the generation of unidirectional electron circulation in molecules by means of circularly polarized ultraviolet (UV) laser pulses [I. Barth, J. Manz, Angew. Chem. 118 (2006) 3028; Angew. Chem., Int. Ed. 45 (2006) 2962], allowing to apply similar methods for the laser driven wavepacket dynamics. It is demonstrated here by means of quantum simulations of the laser driven wavefunction
Ψ(t) of the model system
![View the MathML source View the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6TFM-4RYNMJ9-1-H5/0?wchp=dGLzVlz-zSkzk)
, where
Ψ(t) is expanded in terms of vibrational eigenfunctions
Ψvl which are labeled by quantum numbers
b67e188e0ccd6afe7d9ef4facf82">![View the MathML source View the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6TFM-4RYNMJ9-1-H8/0?wchp=dGLzVlz-zSkzk)
for the vibrations (
v) including the symmetric stretch (
s), bend (
b), antisymmetric stretch (
a), and for the pseudorotation (
l). The corresponding vibrational and pseudorotational eigenenergies and matrix elements for the model
114CdH2 are adapted as approximations from accurate values which have been determined previously, for simulations of high resolution IR spectra. These dipole matrix elements and related selection or propensity rules imply dominant ladder climbing
![View the MathML source View the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6TFM-4RYNMJ9-1-HB/0?wchp=dGLzVlz-zSkzk)
or
00→1-1→2-2→![cdots, three dots, centered cdots, three dots, centered](http://www.sciencedirect.com/scidirimg/entities/22ef.gif)
, i.e., sequential populations of the states with increasing quantum numbers for the bends and pseudorotations
![View the MathML source View the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6TFM-4RYNMJ9-1-HD/0?wchp=dGLzVlz-zSkzk)
, where
17b72ff" title="Click to view the MathML source" alt="Click to view the MathML source">l=+vb or
l=-vb depending on the right (+) or left
(-) circular polarization of the IR laser pulse, respectively.