Electron impact emission spectroscopy

A more precise group of methods measure the beam equivalent pressure in molecular beams near the substrate or the atom fraction of interest in the gas phase. There are several ways of doing this including electron impact emission spectroscopy (EIES), conventional ionization gauges, mass spectrometers, glow-discharge optical spectroscopy, and other methods. We will briefly consider these four in turn. 

Emission Spectroscopy.— The electron impact emission spectra of HC=P+ and DC P+ have been observed. ... 

Analytical electron microscopy by x-ray emission spectroscopy can be extremely useful as a qualitative analysis tool, e.g. to determine which elements are present in lOnm diameter areas of the specimen. However, the greatest impact of AEM comes from quantitative chemical profiles across minute regions or features in the specimen, information that usually cannot be obtained by other means. 

NMR) [24], and Fourier transform-infrared (FT-IR) spectroscopy [25] are commonly applied methods. Analysis using mass spectrometric (MS) techniques has been achieved with gas chromatography-mass spectrometry (GC-MS), with chemical ionisation (Cl) often more informative than conventional electron impact (El) ionisation [26]. For the qualitative and quantitative characterisation of silicone polyether copolymers in particular, SEC, NMR, and FT-IR have also been demonstrated as useful and informative methods [22] and the application of high-temperature GC and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) is also described [5]. 

A brief review and reassessment of data on the photophysics of benzene has been presented by Pereira. Evidence for the l E2g valence state has been obtained by u.v. two-photon spectroscopy.Slow electron impact excites fluorescence in thin films of benzene at 77 K as well as emission from isomers." The fluorescence yields and quenching by chloroform of alkyl-benzenes and 1-methylnaphthalene after excitation into Si, Sz, and S3 states and after photoionization have been measured. The channel-three process has been reconsidered in terms of the effects of local modes and Morse oscillator potentials. Excited-state dipole moments of some monosubstituted benzenes have been estimated from solvent effects on electronic absorption spectra, Structural imperfections influence the photochemistry of durene in crystals at low temperatures. Relaxation time studies on excited oxido-substituted p-oligophenylenes have been made by fluorescence depolarization... 

Of course, the electron-impact source cannot be used if nonvolatile inorganic samples such as metal alloys or ionic residues are to be analyzed. These substances can be investigated using a different kind of ionization chamber called a spark source, similar to the excitation sources used in emission spectroscopy (Chap. 11). The other parts of the spectrometer can be the same as a general-purpose instrument however, a Mattauch-Herzog double-focusing instrument is preferred (Fig. 16.7 below), because the spark source produces ions with a wide spread of kinetic energies. The entire device is known as a spark-source mass spectrometer (SSMS). 

The technique of reducing the Doppler width by the collimation of mo lecular beams was employed before the invention of lasers to produce light sources with narrow emission lines [389]. Atoms in a collimated beam were excited by electron impact. The fluorescence lines emitted by the excited atoms showed a reduced Doppler width if observed in a direction perpendicular to the atomic beam. However, the intensity of these atomic beam light sources was very weak and only the application of intense monochromatic, tunable lasers has allowed one to take full advantage of this method of Doppler-free spectroscopy. 

Auger electron spectroscopy (AES), which involves the electron impact ionization of an atom to give an excited electronic state that decays by emission of a second electron whose energy is characteristic of the atom. This is most commonly used in surface analysis. 

Fundamental quantities, such as wavelengths and transition probabilities, determined using spectroscopy, for atoms and molecules are of direct importance in several disciplines such as astro-physics, plasma and laser physics. Here, as in many fields of applied spectroscopy, the spectroscopic information can be used in various kinds of analysis. For instance, optical atomic absorption or emission spectroscopy is used for both qualitative and quantitative chemical analysis. Other types of spectroscopy, e.g. electron spectroscopy methods or nuclear magnetic resonance, also provide information on the chemical environment in which a studied atom is situated. Tunable lasers have had a major impact on both fundamental and applied spectroscopy. New fields of applied laser spectroscopy include remote sensing of the environment, medical applications, combustion diagnostics, laser-induced chemistry and isotope separation. 

Removal of the Iti electron from NH(X S ) leads to the ionic ground state X removal of the 3a electron to the excited ionic states a A B A, and C Only a few experimental data for the first, third, and fourth ionization potentials Ej of gaseous NH are available. Resonance-enhanced multiphoton ionization (REMPI) of NH coupled with photoelectron spectroscopy (PES) yielded the most accurate results so far [1] and confirmed the values for the first E, obtained by electron-impact mass spectrometry (EIMS) [2] and by He I PES of NH [3]. Values for the second and third Ej to be observed in the He I PES of NH were predicted [3] from the optical emission spectra of NH [4]. Adiabatic and vertical Ej s (in eV) are compared in the following table ... 

Collision-induced vibrational relaxation was studied on vibrationally excited NH(X produced by pulsed electron impact on N2-H2 or N2-H2-Ar gaseous mixtures time-resolved IR Fourier transform spectroscopy was used to observe the v = 3 2, 2 1, and 1 0 fundamental band emission (2500 to 3400 cm ) which allowed the time-dependent vibrational populations to be determined. The following rate constants for v v-1 transitions, were derived at room temperature for the collision partners N2, Ar, and H2 [1] ... 

Classical emission spectroscopy is based on excitation of atoms or molecules into higher electronic states by electron impact (in gas discharges), photon absorption or thermal excitation at high temperatures (in star atmospheres). Excitation by narrow-band lasers may result in the selective... 

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