Measurement of nanoparticle temperature in a (CO 2 ) N cluster beam using SF 6 molecules as tiny probe thermometers
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Measurement of Nanoparticle Temperature in a (CO2)N Cluster Beam Using SF6 Molecules as Tiny Probe Thermometers G. N. Makarova,* and A. N. Petina,b a
Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow oblast, 142190 Russia Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow oblast, 142190 Russia *email: [email protected]
b
Received September 9, 2009
Abstract—A temperature measurement technique using SF6 molecules as tiny probe thermometers is described, and results are presented, for large (CO2)N van der Waals clusters (with N ≥ 102) in a cluster beam. The SF6 molecules captured by (CO2)N clusters in crossed cluster and molecular beams sublimate (evaporate) after a certain time, carrying information about the cluster velocity and internal temperature. Experiments are performed using detection of these molecules with an uncooled pyroelectric detector and infrared mul tiphoton excitation. The multiphoton absorption spectra of molecules sublimating from clusters are com pared with the IR multiphoton absorption spectra of SF6 in the incoming beam. As a result, the nanoparticle temperature in the (CO2)N cluster beam is estimated as Tcl < 150 K. Timeofflight measurements using a pyroelectric detector and a pulsed CO2 laser are performed to determine the velocity (kinetic energy) of SF6 molecules sublimating from clusters, and the cluster temperature is found to be Tcl = 105 ± 15 K. The effects of various factors on the results of nanoparticle temperature measurements are analyzed. The potential use of the proposed technique for vibrational cooling of molecules to low temperatures is discussed. DOI: 10.1134/S1063776110040035
characterization and cluster temperature measure ment is an important area of research.
1. INTRODUCTION Clusters and nanoparticles have been the subject of numerous studies [1–8]. (It should be noted here that nanoparticles are Nparticle clusters with N ≥ 102.) Great scientific and practical interest in clusters and nanoparticles is due to their unique properties and sizedependent effects, as well as to their use in the fabrication of fast microelectronic devices and enhanced memory systems, thinfilm deposition, syn thesis of new materials, and surface processing [1–5]. Metal clusters and nanocomposites are of particular interest in the current search for new hightempera ture superconductors [6, 9, 10]. The use of clusters and nanoparticles for these purposes should be based on knowledge of their physical, chemical and thermody namic properties. One of the most important physical parameters of clusters and nanoparticles is their internal tempera ture. The temperaturedependent characteristics of clusters include polarizability, magnetic moment, ion ization potential, optical response, structure, configu ration, and phase state (e.g., see recent review in [7] and references therein). Cluster temperature strongly affects physicochemical processes involving clusters and cluster beams, in particular fragmentation, evap ora
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