Quantum Dynamical Aspects of Rotationally and Vibrationally Mediated Photochemistry in Matrices and at Surfaces: HCl/DCl in Ar, and NH3/ND3 at Cu(111)

Rotational and vibrational HCl wavefunction upon photodissociation in Ar matrix

Jörn Manz, Peter Saalfrank, and Burkhard Schmidt

In this paper, we investigate two extensions of the concept of vibrationally mediated chemistry, from small molecules in the gas phase to small molecules in matrices and at surfaces. Exemplarily, we consider the systems HCl/DCl in Ar, and NH3/ND3 at Cu (111). The transition from isolated systems to the condensed phase calls for new quantum dynamical techniques, and it allows to predict new phenomena. For the case of matrix isolation, we propagate three-dimensional wavepackets representing photodissociated H- or D-atoms which penetrate from the initial cage into the lattice provided by the matrix. The cage exit probabilities are found to depend not only on the initial vibrational, but also on the rotational states, due to the environmental (Oh) symmetry provided by the (fcc) lattice of the matrix. As a consequence, we suggest the extension from vibrationally to rotationally, or rovibrationally mediated chemistry for matrix isolated molecules. For the case of molecules at surfaces, we adopt Gadzuk's jumping wavepacket plus incoherent averaging scheme, applied to an extended two-dimensional Antoniewicz-type model for the surface-molecule bond plus the vibrational coordinate which lends itself to preferential vibrational excitation, (here the umbrella mode of ammonia). The desorption depends selectively on the initial vibrational state. As a consequence, we suggest the extension of traditional desorption induced by electronic transitions (DIET) to a vibrationally mediated IR+UV DIET scheme which may be used e.g. for enrichment of specific isotopomers at surfaces.

J. Chem. Soc. Faraday Trans. 93 (5), 957-967 (1997)

Movies available

Photodissociation of molecules in matrices

Note: To enhance the visibility of the photodissociation quantum dynamics, only one octant of the rare gas matrix and of the wavepacket is displayed in the movies linked below. The matrix is truncated beyond the shell of the third-nearest neighbors. Cage exit probability after 15 fs is also indicated.


Courtesy by Markus Miertschink (using AVS software)