CARS investigation of collisional shift of the hydrogen Q-branch transitions by water at high temperatures

A high-resolution (∼0.1 cm−1) spectroscopic method based on the application of a Fabry–Pérot interferometer to the spectral analysis of the coherent anti-Stokes Raman scattering (CARS) signal from an individual Raman transition was used to obtain single-shot spectra of hydrogen Q-branch transitions directly in the flame of a pulsed, high-pressure H2/O2 combustion chamber. Simultaneously with the Fabry–Pérot pattern, a broadband CARS spectrum of the complete H2Q -branch structure was recorded in order to measure the temperature of the probe volume. During every cycle of the combustion chamber, a pressure pulse together with single-shot CARS spectra, providing information on individual line shapes and medium temperature, was recorded. On the basis of the experimental data, the temperature dependences of lineshift coefficients for several Q-branch lines of hydrogen molecules under collisions with water molecules were determined in the temperature range 2100 < T < 3500 K, and an empirical ‘fitting law’ for H2H2O lineshift coefficients is proposed