Femtosecond dynamics of Formaldehyde

The photochemistry of formaldehyde has been studied in great detail over many years. The competing multiple dissociation channels from the 1A¹ electronic potential energy surface have been a matter of interest and attained new attention through the recent proposition of a new pathway towards the molecular H₂ and CO products [1]. We apply a UV fs two color transient grating (TG) method to explore the electronic ground and excited state of formaldehyde [2].

[1] D.Townsend, S. A. Lahankar, S. K.Lee, S. D. Chambreau, A. G. Suits, X. Zhang, J. Rheinecker, L. B. Harding, J.M. Bowman, Science , 306, 1158-1161 (2004).
[2] A.M. Walser, M. Meisinger, P.P. Radi, T. Gerber and G. Knopp, (in preparation)

Figure: Potential Energy Surface of H₂CO at the dissociation threshold. The population decay in the 2¹4³ state, observed by the resonant transient grating method is mainly due to collisional relaxation.

Molecular dynamics in the S₁ state of H₂CO has been observed by the frequency dispersed fs-transient grating method. Different delays (see diagrams) between the incoming laser fields give raise to different contributions to the induced polarization and the measured signals reflect different molecular dynamics.

Figure: Dispersed resonant transient grating signals from H₂CO. The selection of specific molecular resonances and the change of the temporal order of interacting laser light pulses (positive and negative time delays) enables the observation of different molecular dynamics.

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