Femtosecond Time-Resolved CARS Spectroscopy on Binary Gas-Phase Mixtures:  A Theoretical and Experimental Study of the Benzene/Toluene System

Abstract

Femtosecond time-resolved CARS measurements on benzene, toluene, and binary mixtures of these molecules have been performed in the gas phase. Whereas a two-pulse excitation process prepares benzene in a single vibrational state, a vibrational wave packet is excited in toluene, which gives rise to oscillatory patterns in the CARS signal. For the mixed system one finds beats between modes coherently excited in both molecules. The results are analyzed using perturbative quantum calculations. It is shown that the rotational degree of freedom is responsible for the decay of the CARS signal in all cases. Furthermore, it is demonstrated that the details of the excitation process have to be incorporated in the calculation to obtain the correct amplitudes of the oscillating signals.

Vibrational polarization beats in femtosecond coherent anti-Stokes Raman spectroscopy: A signature of dissociative pump–dump–pump wave packet dynamics

“…They attributed this decay to vibrationrotation interaction in the case of benzene and decay of spatial orientation in the case of hexatriene. Rubner et al 43 have performed femtosecond CARS on gas phase benzene, toluene, and benzene/toluene mixtures and observed interference between the contributions from different molecules, an effect that had been observed much earlier in liquids. 30,31 In these experiments neither the pump nor the probe is resonant with an excited electronic state, and thus the CARS polarization exists only during the probe pulse.…”

“…5,6,[39][40][41][42][43][44][45][46] Hayden and Chandler 39 performed femtosecond CARS experiments on gas phase benzene and 1,3,5-hexatriene and observed a decay of the signal on a 1-10 ps time scale. They attributed this decay to vibrationrotation interaction in the case of benzene and decay of spatial orientation in the case of hexatriene.…”

Femtosecond time-resolved spectroscopy of elementary molecular dynamics

“…Through this, they were able to increase the selectivity of the probing of the wave packet motion. In the present contribution, we review some recent work on femtosecond time-resolved FWM spectroscopy (Schmitt et al 1997a(Schmitt et al , b, 1998Meyer et al 1997Meyer et al , 1998Meyer et al , 1999Rubner et al 1998;Chen et al 1999a, b, c;Siebert et al 1999Siebert et al , 2000Vierheilig et al 1999). We aim to point out the main advantages of this technique and to emphasize its capability for investigating ground state dynamics.…”

Single-beam coherent anti-Stokes Raman scattering spectroscopy of N2 using a shaped 7 fs laser pulse

“…1 All previous efforts involving CARS of N 2 , O 2 , CO, and H 2 have been based on creating coherence in the medium with separate pump and Stokes pulses, followed by probing of the Raman coherence with a third laser pulse. [1][2][3][4][5] However, the implementation of these measurements with multiple laser beams in harsh chemical environments poses significant challenges for the experimentalist. In particular, it is difficult to maintain the spatial overlap between the beams under high-pressure, high-temperature, and turbulent-mixing conditions.…”