Raman spectroscopy of supersonic jets of CO2: Density, condensation, and translational, rotational, and vibrational temperatures

Abstract

Raman spectroscopy and crystal-field split rotational states of photoproducts CO and H2 after dissociation of formaldehyde in solid argon J. Chem. Phys. 137, 164310 (2012) The links between translational, rotational, and vibrational temperatures of supersonic molecular jets, and their density and degree of condensation, are discussed in terms of quantitative Raman scattering experimental data. Such links are established as the result of energy and momentum conservation laws, and of the collisional regime in the jet. Four representative supersonic expansions of CO 2 , generated at different stagnation pressures are analyzed, showing the potential of quantitative Raman spectroscopy for a complete characterization of the jet.

Experimental and numerical investigation of an axisymmetric supersonic jet

“…Thus, to be comparable, experimental rotational temperatures need to be corrected for condensation. As has been shown recently (Maté et al 1998), from the analysis of the evolution of experimental density number, rotational temperature, and vibrational temperature of several supersonic jets of CO 2 , performed in terms of energy and momentum conservation, relaxation time, and intermolecular binding energy, the condensed gas fraction at each point of the zone of silence can be deduced. The conversion of the energy released by condensation into rotational temperature enhancement is immediate.…”

“…QGDR on-axis rotational temperature is shown in graph 1 of figure 5, to be compared with the rotational experimental temperature corrected for condensation (Maté et al 1998). For z/R e < 10 the calculation overestimates T rot , but for 15 < z/R e < 40 the agreement is excellent.…”

“…So, to show the influence of β the flow field has been recalculated with β = 0.4. Experimental rotational temperature, as measured, and condensation-corrected rotational temperature (Maté et al 1998) are included in figure 3 for comparison.…”

“…Index σ, which refers equally to the QGD or QGDR models, is σ = av for QGD, and σ = tr = rot for QGDR, assumming translational-rotational thermal and pressure equilibrium at the nozzle exit (Maté et al 1998) (AB boundary), and at the BC nozzle wall and CD radial boundaries.…”

“…The parameters ω = 0.93 (Bird 1994), Z ∞ = 17.9 and T * = 100 K (Maté et al 1998) have been used here for CO 2 . At thermal equilibrium p tr = p rot = p av = p, and the QGDR system turns into the one-temperature QGD system with perfect-gas specific heat ratio γ = 7/5.…”