Molecular beam mass spectroscopy

Fig. 51. A RE capacitively-coupled diode with a variety of plasma diagnostics, including Langmuir probe, optical emission spectroscopy, molecular beam mass spectrometry, and ion flux/energy analysis systems. After [35).

The pioneering work of Wilson and co-workers [71-75] established cross-ed-laser and molecular-beam photofragmentation spectroscopy with time-of-flight (TOF) mass-spectrometric detection as a universal and detailed... 

Characterization Tools for Pyrolysis Oils. It wasn t too many years ago that the only tools available to the scientist interested in pyrolysis oil composition were gas chromatography and thermogravi-metric analysis. The complexity of the pyrolysis oils demands high performance equipment, and a list of such equipment mentioned during the symposium would include proton and carbon nuclear magnetic resonance spectroscopy, free-jet molecular beam/mass spectrometry (16.25), diffuse reflectEuice Fourier transform infrared spectrometry ( ), photoelectron spectroscopy ( ), as well as procedures such as computerized multivariate analysis methods (32) - truly a display of the some of the most sophisticated analytical tools known to man, and a reflection of the difficulty of the oil composition problem. 

Combination of Molecular Beam Laser Spectroscopy and Mass Spectrometry... 

The kinetics of the reaction CH3O2 + NO3 was studied by modulated photolysis spectroscopy [7] and later in a discharge flow reactor combined with molecular beam mass spectrometry [8]. In the latter experiment, the CD3O2 radicals were used instead of CH3O2, and their first order decay monitored in the presence of excess NO3 radicals. It was however observed that the first order decay of the methylperoxy radicals did not extrapolate to a common intercept and that the second order plot showed a large positive intercept. This is caused by the regeneration of CH3O2 radicals via reaction... 

The chapter IR Spectroscopic Techniques to Study Isolated Biomolecules gives an overview of some of the most common experimental practices currently in use to characterize the strucmre of isolated biomolecules by infrared spectroscopy. We address especially two main categories of experimental approaches conformation-selective infrared spectroscopy of jet-cooled neutral species and infrared (multiple-photon) dissociation spectroscopy of mass-selected ionized biomolecules. Molecular beam laser spectroscopy methods form the experimental basis for the topics covered in the sixth to eighth chapters. Mass spectrometry-based ion spectroscopy provided the experimental data for the studies reviewed in fourth and fifth chapters (and seventh inpart). 

Detection methods vary with the timescales of the reactions of interest and include pressure measurements, spectroscopy, gas chromatography, and mass spectrometry. Both real-time and postreaction methods are used real-time detection is particulariy useful for short-lived intermediates and can enable a very direct probe of the reaction kinetics, but, compared with postreaction methods, is often quite limited in the number and types of species that can be detected and identified with certainty. Of particular interest in biofuel mechanistic studies are methods capable of discerning between reactive isomers, such as photoionization molecular beam mass spectrometry. ... 

Syage JA, Pollard JE, Cohen RB. 1988. Ultrasensitive detection of atmospheric constituents by supersonic molecular beam, multiphoton ionization mass spectroscopy. El Segundo, CA Aerospace Corp. NTIS No. AD-A202-299. 

L. Zandee, R. B. Bernstein, and D. A. Lichtin. Vibronic/Mass Spectroscopy via Multiphoton Ionization of a Molecular Beam The I2 Molecule. J. Chem. Phys., 69(1978) 3427-3429. 

A molecular beam of XeFj(gas) and a beam of argon ions were directed at the center of a silicon film which had been deposited on a quartz crystal microbalance. The sensitivity of the microbalance was such that the removal of one monolayer of silicon could be detected. In these experiments, the reaction products [e.g., SiF fgas)] were detected using mass spectrometry the surface concentrations were detected using Auger spectroscopy and the rate that material was being removed from the surface was measured with the microbalance. 

The modes of thinking about structures and reactions and intermediates facilitated or even demanded by these conceptual innovations meshed productively with new tools of a different sort to drive the progress of recent decades. Advances in electronics and computers, all sorts of spectroscopy, laser optics and physics, chromatography, mass spectrometry, quantum theory and computational strategies, molecular beam experiments, and so on, radically expanded the limits of experimental and theoretical investigations. 

While one might expect that the techniques developed for photodissociation studies of closed-shell molecules would be readily adaptable to free radicals, this is not the case. A successful photodissociation experiment often requires a very clean source for the radical of interest in order to minimize background problems associated with photodissociating other species in the experiment. Thus, molecular beam photofragment translation spectroscopy, which has been applied to innumerable closed-shell species, has been used successfully on only a handful of free radicals. With this problem in mind, we have developed a conceptually different experiment [4] in which a fast beam of radicals is generated by laser photodetachment of mass-selected negative ions. The radicals are photodissociated with a second laser, and the fragments are detected in coinci-... 

Ultrahigh-vacuum (UHV) surface spectroscopy has been used with molecular beams of SiH4 and mass spectroscopy to elucidate the Si growth mechanism (67, 143). Joyce et al. (67) found that Si growth is preceded by an induction period when surface oxide was removed as SiO. The subsequent film growth proceeds by growth and coalescence of adjacent nuclei with no apparent formation of defects. Henderson and Helm (144) proposed a step-flow model in which adatoms from SiH4 surface reactions difluse to kink sites. 

Molecular-beam epitaxy, for semiconductor growth, with Group 3 nitrides, 12, 4-5 Molecular gyroscopes, via iron carbonyls, 6, 51 Molecular mass distributions, in olefin polymerization, 4,1113 Molecular materials, and crystal engineering, 12, 555 Molecular mechanics future directions, 1, 666 in hybrid computational chemistry, 1, 664 Rh-catalyzed hydroformylation, 7, 239 Molecular modeling, arene chromium tricarbonyls, 5, 255 Molecular orbitals, and photoelectron spectroscopy variations,... 

The present work involves measurement of k in a 0.1 atmosphere, stoichiometric CH -Air flame. All experiments were conducted using 3 inch diameter water-cooled sintered copper burners. Data obtained in our study include (a) temperature profiles obtained by coated miniature thermocouples calibrated by sodium line reversal, (b) NO and composition profiles obtained using molecular beam sampling mass spectrometry and microprobe sampling with chemiluminescent analysis and (c) OH profiles obtained by absorption spectroscopy using an OH resonance lamp. Several flame studies (4) have demonstrated the applicability of partial equilibrium in the post reaction zone of low pressure flames and therefore the (OH) profile can be used to obtain the (0) profile with high accuracy. 

Mass spectroscopy is a common detector in crossed-molecular beam experiments and has also been used in flow systems [17]. Measurements are normally restricted to an analysis of the identity of the reaction products and are not sensitive to the internal energy states of the products. The determination of product translational energy distributions in crossed-molecular beam experiments is usually achieved by placing some form of velocity analyser before the mass spectrometer (see below). 

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