Cluster mass spectrum

Effect of Ionization Energy on Cluster Mass Spectrum... 

Some of the early studies reported abnormal fragmentation patterns when polyatomic molecules were seeded in argon. It was speculated that heteroclusters, such as Ar Xra, are the neutral precursors for the various ions observed in the cluster mass spectrum. Our study of the argon/methanol coexpansions showed that the CMS is definitely affected by the choice of carrier gas, as well as the energy... 

Figure 2 shows the effect of increasing di-deuteriurn concentration upon the iron cluster mass spectrum. The reaction applicable to the loss of the bare cluster spectrum is... 

Thus, mass spectrometry, mainly MALDI MS and ESI MS, has played a major role in identifying clusters of metals like Pt, Pd, Cu and alloy clusters, their composition and structure determination along with other characterization techniques. In case of alloy clusters, mass spectrum is an important tool to know the combination of different metal atoms in a specific cluster. 

Collision-induced dissociation mass spectrum of tire proton-bound dimer of isopropanol [(CH2)2CHOH]2H. The mJz 121 ions were first isolated in the trap, followed by resonant excitation of their trajectories to produce CID. Fragment ions include water loss mJz 103), loss of isopropanol mJz 61) and loss of 42 anui mJz 79). (b) Ion-molecule reactions in an ion trap. In this example the mJz 103 ion was first isolated and then resonantly excited in the trap. Endothennic reaction with water inside the trap produces the proton-bound cluster at mJz 121, while CID produces the fragment with mJz 61. 

Not only the molecular ion peak but all the peaks m the mass spectrum of benzene are accompanied by a smaller peak one mass unit higher Indeed because all organic com pounds contain carbon and most contain hydrogen similar isotopic clusters will appear m the mass spectra of all organic compounds... 

DDT resistant insects have the ability to convert DDT to a less toxic substance called DDE The mass spectrum of DDE shows a cluster of peaks for the molecular ion at m/z 316 318 320 322 and 324 Suggest a reasonable structure for DDE... 

A typical FAB mass spectrum of glycerol alone, showing a protonated molecular ion at m/z 93 accompanied by decreasing numbers of protonated cluster ions (m/z, 1 + nx92 n = 2, 3, 4,. ..). 

The size distribution of the clusters produced in the cluster source is quite smooth, containing no information about the clusters except their composition. To obtain information about, for example, the relative stability of clusters, it is often useful to heat the clusters. Hot clusters will evaporate atoms and molecules, preferably until a more stable cluster composition is reached that resists further evaporation. This causes an increase in abundance of the particularly stable species (i.e., enhancing the corresponding peak in the mass spectrum, then commonly termed fragmentation spectrum ). Using sufficiently high laser fluences (=50 /iJ/mm ), the clusters can be heated and ionized simultaneously with one laser pulse. 

Fig. 6. Mass spectrum of pholoionized C oCa, clusters with high metal content additional edges, interpreted as completion of a third and fourth layer, are observed at. v = 236 and A = 448.

At the end of this section, let us return briefly to the spectra shown in Fig. 3. Notice the structure in the mass spectrum of QoCa, between the completion of the first metal layer at 32 and the second at 104. This structure is identical in the fragmentation mass spectra of fullerenes covered with Ca and with Sr. It is reminiscent of the subshell structure of pure Ca clusters. The subshells could be correlated with the formation of stable islands during the growth of the individual shells[10,l 1]. The sublayer structure we observe here may also give some clue to the building process of these layers. However, the data is presently insufficient to allow stable islands to be identified with certainty. 

Fig. 8. Mass spectrum, with background subtracted, of pbo-toionized (Cfto) Rbv clusters containing both singly and doubly ionized species tbe solid line connects peaks belonging to groups of singly ionized clusters with a fixed value of n. Note tbe dominant peaks corresponding to (C (,Rb, ) Rb and (QoRb,.,) Rb2 (marked...

Fig. 34 Mass spectrum of sulfur clusters obtained by evaporation of liquid sulfur followed by cooling and adiabatic expansion of the vapor [209]. The figures at the peaks give the number of Sg molecules which represent this particular mass...

The fact that only ethylene and tetramethylethylene are evolved from exp-[8]rotane 168 and permethyl-exp-[6]rotane 173 upon thermal decomposition leads to the conclusion that the spirocyclopropane moieties in these expanded [n]rotanes fragment only externally and leave carbene moieties behind. Indeed, the MALDI-TOF mass spectra of several exp-[ ]rotanes show fragment ions with M minus 28. Thus, if this fragmentation in an exp-[n]rotane were to continue n times, a cyclic C carbon cluster would be left over. So far, however, a fragment ion with m/z = 480 corresponding to 182 has not been recorded in the mass spectrum of exp-[8]rotane 168 and it remains to be seen whether a Cgo cluster 183 will be detected in the mass spectrum of exp-[12]rotane 171 (Scheme 35). 

Figure 15. (a) Mass spectrum of alcohol clusters about Li+. Data taken at T = 150 K and (b) same as (a) but with an expanded intensity scale An = Li+(CH30H) Bn = Li+(CH30H) (H20). Taken with permission from ref. 106. 

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