CARS SPECTROSCOPY OF MOLECULES AND CLUSTERS IN SUPERSONIC JETS

Supersonic molecular beams of D//2, CH//4, NH//3, and C//2H//4 are investigated in the expansion region employing coherent anti-Stokes Raman spectroscopy (CARS). The analysis of rotationally resolved CARS spectra allows the determination of temperatures in the beam. The rotational relaxation as a function of stagnation pressure and separation from the nozzle is studied by recording the Q branch for D//2 and the nu //3 R and S branches for CH//4. Rotational temperatures for NH//3 are determined by investigating the complete nu //3 band. At strong stagnation conditions broad structures arise which can be attributed to the formation of NH//3 clusters. For C//2H//4 the nu //5 band with resolved rotational structure is reported. Again, at larger distances from the nozzle, broad structures are observed. They are assigned to the nu //1 and nu //5 vibrations in the C//2H//4 clusters.