Ionization experiment

Weiner J, Masnou-Seeuws F and Guisti-Suzor A, Assooiative ionization experiments, potentials, and dynamios Advances in Atomic, Moiecuiar and Opticai Physics vol 26, ed D Bates and B Bederson (Boston Aoademio) pp 209-96... 

Isotope shifts for most elements are small in comparison with the bandwidth of the pulsed lasers used in resonance ionization experiments, and thus all the isotopes of the analyte will be essentially resonant with the laser. In this case, isotopic analysis is achieved with a mass spectrometer. Time-of flight mass spectrometers are especially well-suited for isotopic analysis of ions produced by pulsed resonance ionization lasers, because all the ions are detected on each pulse. 

The calculation done without including diffuse functions in the basis set fails to find three of the lower excited states. It does still compute excitation energies for six excited states, but the other three states are higher in energy than the 8.75 eV state, and do not correspond to the missing states observed by experiment. The three missing states are Rydberg states, observable via multiphoton ionization experiments. 

Figure 1. Schematic of a two-color resonant two-photon ionization experiment "ZEKE states" lie just below each cation threshold, as indicated by asterisks.

A strict correspondence is also observed between the lcR2PI spectral shifts Avof the selected diastereomeric clusters and the relevant lcR2PI mass fragmentation patterns. In the lcR2PI ionization experiments, some excess energy is imparted to the adduct to an extent which somewhat reflects its HOMO-LUMO energy gap... 

Figure 18. Illustration of the molecular beam-electron beam crossing region used in the electron impact ionization experiments. The molecular beam source, buffer, and hexapole chambers are similar to those shown in Figure 3.

The structures of protonated azoles in the gas phase (equilibrium ) can be determined by mass spectrometry in a chemical ionization experiment followed by collision-induced dissociation. The method has been used to study the protonation of benzimidazole (5), indazole (7), and 1-ethylimidazole (179) (all, as expected, on the pyridinelike nitrogen atoms) (80OMSI44) of 1-ethylpyrrole (probably at the -position) (80OMS144) and indole (at the -position) (85IJM49) (see Section IV.A). 

In many field emission and field ionization experiments, field strength is a basic parameter which has to be known accurately before a lot of experimental data can be interpreted properly. Determination of field strength at the field emitter surface and field distribution above the field emitter surface in field electron and field ion emission, however, is not an easy task because of the complicated geometry of the tip. In field emission, the validity of the Fowler-Norheim theory has been established experimentally to within about 15%, and the current density as a function of the field has been tabulated.26 Thus it is possible to determine the field strength simply from the field emission current density. The field strength so determined cannot of course be more accurate than 15%. 

Transient two-photon ionization experiments on trimer systems were, of course, motivated by a need for time-resolved verification of the pseudorotation motion, which can be considered as a superposition of the asymmetric stretch (Qx) and the bending vibration (Qy) [12]. The triatomic molecule with its three modes is quite different from an isolated oscillating dimer, which vibrates in its single mode until eventually it radiates or predissociates. The interplay of vibrational modes in a trimer system can be considered as the prototype of IVR. 

T. P. Softley The aims of ZEKE spectroscopy are conceptually different from the atomic pulsed-field ionization experiments that predate ZEKE. In the latter, the aim is always to observe and study the individual Rydberg states. In ZEKE spectroscopy the aim is to detect small batches of Rydberg states lying below successive vibration-rotation thresholds of the ion without specific interest in the individual Ryd-... 

B. Kohler My question to T. Softley ties in to one of the major themes of the meeting, namely coherence. In your presentation you briefly mentioned that it may be important to consider an initially coherent superposition of states in the preparation step of experiments on highly excited Rydberg states. Several groups have now prepared coherent electronic wavepackets using picosecond (and shorter) pulses. Would this kind of an initial state be useful for any of the classes of pulsed-field ionization experiments that you have described ... 

Fig. 10.2 Major components of a thermal atomic beam apparatus for microwave ionization experiments,the atomic source, the microwave cavity, and the electron multiplier. The microwave cavity is shown sliced in half. The Cu septum bisects the height of the cavity. Two holes of diameter 1.3 mm are drilled in the side walls to admit the collinear laser and Na atomic beams, and a 1 mm hole in the top of the cavity allows Na+ resulting from a field ionization of Na to be extracted. Note the slots for pumping (from ref. 4).

Figure 1. Early proposal of a unified model for SIMS and other desorption ionization experiments. Reproduced with permission from Ref. 3. Copyright 1983, Elsevier Science Publishers B.V. (First presented at a conference on ion formation from organic solids, Munster, West Germany, 1981.)...

Data will also be given for other desorption ionization experiments which support the general notion of energy... 

The protonated serine octamer (Ser)8H+ is exceptionally stable, with a magic number effect of more than 20. The magic number effect M can be obtained from the mass spectra, by the abundance ratio of the n unit cluster compared with the n 1 and n+1 unit cluster, by the relationship M=2In/(In 1+In+1). Electrospray mass ionization experiments [98], performed on 0.1 M solutions of L-serine and d-[[13]C] Serine, show a strong preference toward the formation of homochiral protonated clusters (L-Ser)8H+ and (D-[13C]Ser)8H + instead of the heterochiral analogs (L-Ser)n (D-[13C]Ser)8 — nH+ (n 1 7). The same trends are obtained in deuterium-labeling... 

The peak of the intensity of the circularly polarized light is half of that of the linearly polarized light. But this is not sufficient for the effective laser intensity in the ionization experiments. A factor of 0.65 has been estimated on the basis of the ADK calculation of Xe ionization rates [27]. The factor, 0.75 was experimentally obtained here by comparing the Isat of Xe for linearly polarized light to that for circularly polarized light [12]. 

At present, the low-lying states of Na2 are better characterized computationally than experimentally, although multiphoton ionization experiments may change that picture eventually. We find reasonably close agreement between the results of our all-electron computations, pseudopotential (10), and model potential (11) computations. The latter two kinds of computations may give more accurate results than our ab initio computations since they may account for at least certain core polarization effects. 

Using an apparatus of the type shown in Fig. 7.1, Bayfield and Koch (1974) conducted an ionization experiment with hydrogen Rydberg atoms that were prepared in the band 63 < tiq < 69 and exposed to electromagnetic radiation of three different frequencies Wj = 2nfi, with fi = 30 MHz,... 

Fig. 7.1. Schematic sketch of a typical microwave ionization experiment.

While for a long time microwave ionization experiments addressed the linear polarization (LP) case only, experimental results on elliptic polarization (EP) are now available from Stony Brook (Koch and van Leeuwen (1995), Bellermann et al. (1996)). According to a widely used rule-of-thumb, EP ionization thresholds are expected to be higher than LP ionization thresholds. Bellermann et al. have shown that this is not generally the case. Bellermann et al. also provide experimental evidence for the importance of classical phase-space structures in the EP case. The EP case adds a new dimension to the microwave ionization problem. It provides an additional testing ground for the manifestations of chaos in atomic physics. 

Meurer and Eberlin reported that the Meerwein reaction (Scheme 14) occurs efficiently at atmospheric pressure in a mass spectrometer in electrospray ionization (ESI) and chemical ionization experiments <2006JMP470>. The technique permits the analysis of high molecular weight thiiranes whose volatility is too low to fill the chamber under normal vacuum conditions. The acylium ion used was Mc2NCO, formed from the dopant tetramethylurea. An earlier study on the Meerwein reaction in a mass spectrometer was reported <2004JAM398>. 

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