CARS spectroscopy of molecules and clusters in supersonic jets

Barth, Hans-Dieter; Jackschath, C.; Pertsch, Thomas; Huisken, F.

doi:10.1007/bf00687148

Cited by 18 publications

(3 citation statements)

References 40 publications

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“…Clustering can significantly influence both the terminal energy and the terminal energy spread of a supersonic beam and its characterization is therefore obligatory, if for no other reason than to delimit and avoid the clustering regime. There exists an extensive literature on the clustering of ammonia in both neat and seeded beams, including basic mass spectrometrometric studies, 14,15 cluster spectroscopy, 15,16 photodissociation of clusters, 17-20 characterization of cluster fragmentation upon electron impact, 21,22 ultraviolet ͑UV͒ photoelectron spectroscopy of clusters, 23 vibrational excitation of clusters through helium atom impact, [24][25][26] electron diffraction studies of solid clusters, 27 and spectroscopy of ammonia on or in larger inert gas clusters. 28,29 Some time-of-flight ͑TOF͒ 30 energy analysis of clustered ammonia seeded beams has been carried out by the Buck and co-workers 22,25,26 within the context of crossed-beam scattering experiments.…”

Section: Seeded Beams Of Ammonia In Heliummentioning

confidence: 99%

Selected energy epitaxial deposition of GaN and AlN on SiC(0001) using seeded supersonic free jets of NH3 in helium

Torres

Doak

Wilkens

et al. 1999

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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By expanding a gas mixture into vacuum through a supersonic nozzle, a heavy “seed” species in a light diluent gas can be aerodynamically accelerated to suprathermal translational energies. Such beams are intense, directional, easily tuneable in energy, and narrowly distributed in energy. They thereby offer the means of selectively promoting activated gas-surface reactions. We report the use of 10% NH3 in He seeded beams to grow GaN and AlN epitaxially on 6H–SiC(0001) and to grow GaN on AlN buffer layers deposited on SiC(0001). The III–N films were grown under a variety of incident energies and angles of the NH3 beam, with the III metal species supplied from an effusive evaporator source. Film thickness and morphology were characterized ex situ with Rutherford backscattering spectroscopy, Auger spectroscopy, transmission electron microscopy, and atomic force microscopy. Of particular relevance to the III–N growth are the following results: (1) Selected energy epitaxial growth was observed, evidently via a direct reaction channel over a barrier of 0.25±0.1 eV. A comparison of films grown at 0° (normal) and 30° angles of NH3 incidence indicated total energy scaling of this chemisorption process. (2) A low energy reaction channel (<0.10 eV) was explicitly confirmed. The mechanism by which this might occur is discussed.

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Section: Seeded Beams Of Ammonia In Heliummentioning

confidence: 99%

Selected energy epitaxial deposition of GaN and AlN on SiC(0001) using seeded supersonic free jets of NH3 in helium

Torres

Doak

Wilkens

et al. 1999

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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“…[6] , C2H4 [7] , and HCN [8] complexes. The assignment of the new features to dimers or polymers was based on the analysis of the shifts of the band centers with respect to the monomer transitions.…”

Section: Introductionmentioning

confidence: 99%

“…However, all attempts to apply Raman technique in similar purposes did not manifest similar spectacular progress up to now. In a few years a number of coherent Raman spectra have been obtained for H20 [3] , HC1 [4] , C02 [5] , NH3 [6] , C2H4 [7] , and HCN [8] complexes. Later Nibler et al [2] observed CARS spectra of the associating carbon dioxide, enabling them to draw preliminary conclusions on the structure of (C02)2 dimers.…”

Section: Introductionmentioning

confidence: 99%

CARS spectroscopy of carbon dioxide associating in free jet expansions

et al. 1994

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IntroductionThe measurement of microwave and IR high resolution spectra in freely expanding jets has become almost a routine. However, all attempts to apply Raman technique in similar purposes did not manifest similar spectacular progress up to now. First estimates demonstrating sufficient sensitivity of the nonlinear CARS technique for the studies of molecular association in a jet have been performed by Byer and co-workers [1 ] . Later Nibler et al. [2] observed CARS spectra of the associating carbon dioxide, enabling them to draw preliminary conclusions on the structure of (C02)2 dimers. In a few years a number of coherent Raman spectra have been obtained for H20 [3] , HC1 [4] , C02 [5] , NH3[6] , C2H4 [7] , and HCN [8] complexes. The assignment of the new features to dimers or polymers was based on the analysis of the shifts of the band centers with respect to the monomer transitions. It is well known that in the spectra of hydrogen bonded species these shifts amount to more than several tens of wavenumbers. Therefore, in the spectra of HCN polymers, for example, the attribution of newly appearing bands can be performed even without detailed analysis of their vibro-rotational structure. Significantly weaker intermolecular interaction in C02 dimers results in very small frequency shifts. Accordingjto [9, 10] the shifts of JR active transitions amounts to +1 .628884 cm1 for V3 C02 band, -1 .29 cm for 2v2 +V3 and -0.85 cm1 for vi + V3 bands.An assignment of a new band at 1 28 1 cm1 in the CARS spectrum of an expanding C02 +He mixture to the low frequency Fermi dyad member of (C02)2 has been suggested first in [2] . Recently Nibler et.al. [11] have revised this attribution. They have shown that the first evidences of molecular association appear on the wing of monomeric Q branch as a group of closely and irregularly spaced lines concentrated within ca. 1 cm from the Q branch center vi = 1285.4 cm. The increase in stagnation pressure up to = 14 atm causes the growth of a very complicated structure concentrated in the vicinity of 1281 cm , which has been refered earlier to dimeric band. Further changes of the CARS spectrum with increasing stagnation pressure relate with an appearance of a new band at 1275.5 cm1, surely belonging to large clusters or condensed phase in bulk. In this work we communicate new results of our CARS observations and their theoretical modeling aimed to the detection of dimeric O-8194-7504-9/94/$6.oo SPIE Vol. 2205 High-Resolution Molecular Spectroscopy (1993) / 95 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/26/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspxcarbon dioxide associates. To perform preliminary analysis we have developed a kinetic scheme of dimer formation in expansions of pure carbon dioxide or its mixture with rare gas through the slit or round orifice. The on-axis distributions of (C02)2 dimeric concentrations calculated so far enabled us to choose optimum focusing of the laser beams and to restrict the stagnation pressures to the val...

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Infrared Vibrational Predissociation Spectroscopy of Small Size‐Selected Clusters

Huisken¹

1991

Advances in Chemical Physics

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CARS spectroscopy of molecules and clusters in supersonic jets

Cited by 18 publications

References 40 publications

Selected energy epitaxial deposition of GaN and AlN on SiC(0001) using seeded supersonic free jets of NH3 in helium

Selected energy epitaxial deposition of GaN and AlN on SiC(0001) using seeded supersonic free jets of NH3 in helium

CARS spectroscopy of carbon dioxide associating in free jet expansions

Infrared Vibrational Predissociation Spectroscopy of Small Size‐Selected Clusters

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