Molecular synchrotron

FIGURE 14.16 (a) Schematic of a molecular synchrotron. The synchrotron consists of two hexapole half-rings with a 12.5 cm radius, separated by a 2 mm gap. (b) Density of ammonia molecules at the detection zone inside the synchrotron as a function of storage time for up to the 40th round trip. Expanded views of two TOP profiles are shown in the insets, illustrating the narrow widths of these peaks. (From Heiner, C.E., Nature Phys., 3, 115-118, 2007. Copyright MacMillan Publishers Ltd. With permission.)... 

In the crossed-beam geometry, the particles encounter each other only once. Alternatively, the decelerated beams can be loaded into a molecular synchrotron, located at the intersection point of the two molecular beams. In a synchrotron containing 20 counterpropagating packets, a packet that completed 100 round trips would have undergone 4000 encounters. We are currently constructing a molecular synchrotron as a collider for neutral polar molecules, which is designed to be combined with the crossed-beam apparatus. 

Heiner CE, Carty D, Meijer G, Bethlem HL. (2007) A molecular synchrotron. Nature Physics 3 115-118. 

Yang X, Lin J, Lee Y T, Blank D A, Suits A G and Wodtke A M 1997 Universal crossed molecular beams apparatus with synchrotron photoionization mass spectrometric product detection Rev. Sc/. Instrum 68 3317-26... 

The method involves the irradiation of a sample with polychromatic X-rays (synchrotron radiation) which inter alia promote electrons from the innermost Is level of the sulfur atom to the lowest unoccupied molecular orbitals. In the present case these are the S-S antibonding ct -MOs. The intensity of the absorption lines resulting from these electronic excitations are proportional to the number of such bonds in the molecule. Therefore, the spectra of sulfur compounds show significant differences in the positions and/or the relative intensities of the absorption lines [215, 220, 221]. In principle, solid, liquid and gaseous samples can be measured. 

NIS of synchrotron radiation yields details of the dynamics of Mossbauer nuclei, while conventional MS yields only limited information in this respect (comprised in the Lamb-Mossbauer factor /). NIS shows some similarity with Resonance Raman- and IR-spectroscopy. The major difference is that, instead of an electronic resonance (Raman and IR), a nuclear resonance is employed (NIS). NIS is site-selective, i.e., only those molecular vibrations that contribute to the overall... 

By using NFS, information on both rotational and translational dynamics can be extracted. In many cases, it would be favorable to obtain separate information about either rotational or translational mobility of the sensor molecule. In this respect, two other nuclear scattering techniques using synchrotron radiation are of advantage. Synchrotron radiation-based perturbed angular correlations (SRPAC) yields direct and quantitative evidence for rotational dynamics (see Sect. 9.8). NIS monitors the relative influence of intra- and inter-molecular forces via the vibrational density of states (DOS) which can be influenced by the onset of molecular rotation (see Sect. 9.9.5). 

In this chapter we have discussed the successful implementation in our laboratory, for the first time, of the soft (i.e. low energy) electron-impact ionization method for product detection in crossed molecular beams reactive scattering experiments with mass spectrometric detection. Analogous to the approach of soft photoionization by tunable VUV synchrotron radiation,... 

Doucet, J. (2003), New synchrotron radiation-based imaging techniques and archaeology, Phys. Chem. 117 (Molecular and Structural Archaeology Cosmetic and Therapeutic Chemicals) 179-192. 

An interesting feature of polarized IR spectroscopy is that rapid measurements can be performed while preserving molecular information (in contrast with birefringence) and without the need for a synchrotron source (X-ray diffraction). Time-resolved IRLD studies are almost exclusively realized in transmission because of its compatibility with various types of tensile testing devices. In the simplest implementation, p- and s-polarized spectra are sequentially acquired while the sample is deformed and/or relaxing. The time resolution is generally limited to several seconds per spectrum by the acquisition time of two spectra and by the speed at which the polarizer can be rotated. Siesler et al. have used such a rheo-optical technique to study the dynamics of multiple polymers and copolymers [40]. 

The question also arises as to where the chiral molecules came from. Were the L-amino acids or the D-sugars selected on the primeval Earth, or are exuaterresuial sources responsible for the homochirality This second possibility is dealt with by hypotheses on the effect of circularly polarised light, of extraterrestrial origin, on chiral molecules in the molecular clouds from which the solar system was formed. One such hypothesis was proposed by Rubenstein et al. (1983) and developed further by others, particularly A. W. Bonner (Bonner and Rubenstein, 1987) both scientists worked at Stanford University. The authors believe that the actual radiation source was synchrotron radiation from supernovae. The excess of one enantiomeric form generated by this irradiation process would have needed to be transported to Earth by comets and meteorites, probably during the bombardment phase around 4.2-3.8 billion years ago. 

In this chapter, we briefly discuss the theoretical background of polarized x-ray absorption spectroscopy (PXAS). Many of the recent applications of synchrotron radiation to polarized absorption edge structure and to EXAFS are discussed, with particular emphasis being given to the study of discrete molecular systems. We present here some indication of the potential applications of PXAS to systems of chemical and biological interest. 

The study of the photoionization cross section as a function of photon energy for the different orbitals of Me4Sn, which can be a powerful tool for the assignment of the spectra and the analysis of the contribution of the various atomic orbitals to the molecular orbitals, has been carried out by the authors of References 11 and 12 by using He I and He II as ionizing source, and of Reference 13 by using synchrotron radiation. Bertoncello... 

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