Time‐resolved investigation of the ν 1 ro‐vibrational Raman band of H 2 CO with fs‐CARS

• Published in: Journal of Raman spectroscopy 2007-02, Vol.38 (2), p.147-153
• Main Authors: Walser, A. M., Beaud, P., Radi, P. P., Tulej, M., Gerber, T., Knopp, G.
• Format: Article
• Language: English
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/jrs.1613

The technique of femtosecond time‐resolved coherent anti‐Stokes scattering (fs‐CARS) is used to investigate the strongly perturbed ν 1 ro‐vibrational Raman band of formaldehyde (H 2 CO). The time‐dependent signal is simulated using a ‘Watson‐’Hamiltonian in A‐type reduction and Raman theory for asymmetric rotors. The results are compared with the experimental data. The fs‐CARS method measures the evolution of the polarization in a molecular ensemble via superposition of many states and is sensitive to spectral irregularities or line shifts of the involved transitions. ‘Coriolis’ interactions play a major role in the analysis of the ν 1 band of formaldehyde. We successfully simulate the fs‐CARS transient signal from the ν 1 band of formaldehyde including a model for multiple ‘Coriolis’ interactions, without the necessity of describing the complete interaction between all the vibrational levels. ‘Coriolis’ coupling coefficients and energy shifts are derived from the experiment by a least‐square fit. The results are discussed and compared to literature values. Copyright © 2006 John Wiley & Sons, Ltd.