Diode-laser spectroscopy of supersonic free jets

Lineshape analysis of stimulated Raman spectra of the near‐nozzle region of free jet expansions

“…As the monomer fraction decreases, the lineshape begins to deviate from the Gaussian form, getting flatter on top and then splitting and showing a double peak structure. A similar trend in the lineshape evolution was obtained in NH 3 expansions with increasing stagnation pressures, [4,5] which is equivalent to increasing the aggregation. Note that the flanks of the profile simulated in Fig.…”

“…A similar lineshape with a double peak structure was reported previously in infrared absorption [4,5,11] and FTMW [8,21] measurements on supersonic expansions, and was attributed exclusively to the effect of strong condensation on the jet axis. The lineshape we present here has a different origin, though our simulation can reproduce the just mentioned results including some degree of condensation, as it will be shown.…”

“…A lineshape with a double peak structure has been also reported in works on infrared absorption spectroscopy in supersonic expansions. It was first observed in NH 3 expansions, [4] described as a clear deviation of the Gaussian form, with a splitting that appears and becomes more pronounced with increasing stagnation pressure. This line profile was finally attributed [5] to clustering that is concentrated on the axis and depletes the proportion of monomers with Doppler shift around zero, yielding a dip in the absorption profile.…”

“…Among them, highresolution spectroscopic techniques, such as visible absorption, [3] diode-laser infrared absorption, [4,5] Fourier transform infrared (FTIR) absorption spectroscopy, [6,7] Fourier transform microwave (FTMW) measurements, [8] resonance enhanced multiphoton ionization (REMPI), [9,10] cavity ring down spectroscopy, [11] or nonlinear Raman spectroscopies (stimulated Raman Spectroscopy (SRS), CARS, etc), [12,13] have been widely used to measure vibrationrotation spectra of molecules cooled in the expansion and for the analysis of phenomena naturally occurring, or externally induced, in free jets and supersonic beams, like nonequilibrium between the molecular degrees of freedom, [9,10] nucleation and clustering of the gas, [11,12] photodissociation and photon-induced reactions, [14,15] or interactions of molecules with fields. [16] In the spectra obtained from jets with techniques that have a great field depth, like infrared absorption, the measured intensity and the profile of the spectral lines are the result of an integration along the line of sight, containing information about the density, temperature, and velocity of the observed particles within the jet.…”

Critical assessment: Use of supersonic jet spectrometry for complex mixture analysis (IUPAC Technical Report)

“…In a similar manner, it is possible to measure the heat generated by laser excitation using a bolometer, placed downstream [12][13][14]. Coherent anti-Stokes Raman spectroscopy [15], diode laser infrared absorption spectroscopy [16], and cavity ringdown laser absorption spectroscopy [17,18] are also used for sample detection. A stimulated emission pumping technique has been developed for high-resolution spectroscopy and lifetime measurement of the ground electronic state, in which the second laser is used for excitation, followed by a fluorescence measurement or for multiphoton ionization [19,20].…”