1,720,976 research outputs found
An Opto-Thermal Study of NH3 Rotational Relaxation in NH3-He Supersonic Expansions
No full textWe have investigated the rotational relaxation of NH3 in NH3-He supersonic expansions by means of opto-thermal spectroscopy. Molecules are excited in the v3 + v4 band, around 5100 cm -1, using the third Stokes line of a Raman-shifted pulsed laser. Rotational distributions are measured for different values of the source stagnation pressure and NH3 concentration. At low rotational temperatures, populations deviate from a Boltzmann distribution. This is attributed to the reduction of para-to-ortho conversion during the expansion
Molecular beam diagnostics by means of fast superconducting bolometer and pulsed infrared laser
No full textThe laser-bolometric infrared spectroscopy is an efficient method for measuring the internal energy distributions of molecular beams. Additional informations about the kinetic energy distribution of molecules in a selected internal state can be obtained from time resolved experiments. A fast superconducting bolometer and a pulsed infrared CO2 laser have been used for testing the use of this technique as a universal tool for molecular beam diagnostics. Experimental results are presented and analyzed for pure SF6 and helium seeded with 5% SF6 beams. The efficiency of fast superconducting bolometers, used for molecular beam time-of-flight measurements, is discussed. A comparison is made between time resolved laser-bolometric technique and alternative molecular beam diagnostic methods
Infrared multiple-photon absorption of SF6 and CF3Br in a variable temperature molecular beam
No full textThe molecular beam opto-thermal infrared spectroscopy [l] has been recently applied for studying the infrared multiple-photon absorption (M.P.A.) of polyatomic molecules [2J. The main advantage of this method, compared with conventional cell experiments, is the complete removal of collisional effects. The low density molecular beam virtually eliminates other sources of systematic error like, for example, the self-focusing and de-focusing of the laser beam which is sometimes observed in cell experiments [3]. Moreover the molecular beam technique has the following unique feature: it is possible to prepare molecules with different distributions of rovibronic states. We shall show later how this last property may be used for studying the effect of the initial distribution of internal energy on the M.P.A. process. The experimental apparatus and the detection system are described elsewhere [2,4]. In the present configuration, the molecular beam is produced by expanding pure SF` or CF^Br seeded in He through a variable-temperature supersonic nozzle (diameter 75 ±_ 5μm). The temperature may be set from about 100 K to 500 K and is stabilized within 0.1 K. The IR pulsed source is a Lumonics TEA 820 line-tunable CO2 laser. The laser fluence may be varied by means of a suitable optical system and is measured by a Scientech powermeter. The molecular beam energy distribution may be varied by changing both the pressure and the temperature of the source. The translational energy distribution has been determined by time-of—flight measurements [4]
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Add a signal averaging facility to your laboratory microcomputer
No full textWe have developed a simple interface which adds an analogue signal averaging facility to any Z80-based microcomputer. The maximum sampling rate is 5 MHz with 8 bits resolution and the maximum memory length is 2048 channels. The interface communicates with the microcomputer through a simple parallel input-output circuit. Data acquisition is handled in parallel with the normal operation of the microcomputer. This paper describes in detail the interface hardware while a listing of the computer program is available from the authors
Collisionally aligned molecular beams: a tool for stereodynamical studies in the gas phase and at surfaces
No full textProduction, characterization and control of alignment degree of molecules are of importance for investigating in detail the stereodynamics of elementary processes involving elastic, inelastic and reactive events and also to prepare gas-phase species for selective surface scattering investigations. The focus here is on collisional alignment in supersonic seeded molecular beams, a technique which shows perspectives on the applications, offering appealing features for 'duty cycle' and intensity characteristics. Attention will be addressed to recent stereodynamical studies carried out on hydrocarbon molecules in the gas phase and on applications of such aligned beams to surface scattering studies
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