Neutral collisional activation

Neutral Collisional Activation and Angle-Resolved NRMS. 89... 

NCR Neutralization-collisional activation-reionization NDMA N,N-Dimethylaniline... 

Collision-induced dissociation (or decomposition), abbreviated CID. An ion/neutral process wherein the (fast) projectile ion is dissociated as a result of interaction with a target neutral species. This is brought about by conversion during the collision of part of the translational energy of the ion to internal energy in the ion. The term collisional-activated dissociation (or decomposition), abbreviated CAD, is also used. 

The major fragmentation in mass spectra of 1,2,5-oxadiazoles is attributed to the loss of nitrile and nitrile oxide or expulsion of NO. The conversion of 3,4-dicyano-l,2,5-oxadiazole-2-oxide (3,4-dicyanofuroxan) 10 to cyanogen iV-oxide 11 (Equation 5) was investigated under the conditions of collisional activation (CA) and neutralization-reionization (NR) mass spectrometry. Flash vacuum thermolysis mass-spectrometry (FVT-MS) and flash vacuum thermolysis infra-red (FVT-IR) investigations of furoxans 10, 12, and 13 reveal that small amounts of cyano isocyanate accompany the formation of the main thermolysis product 11 <2000J(P2)473>. 

In situ generation and characterization of [C,N2,S] ions (miz 72), formed by dissociative ionization of ionized [l,2,5]thiadiazolo[3,4-f][l,2,5]thiadiazole I , 79, has been made possible for the first time following collisional activation (CA) and neutralization-reionization (NR) mass spectrometry <1997JST(418)209>. 

In the ion-source El spectrum of ClSi(CH3)3, ions of the formal composition [H2,C2,Si]+ have been observed171. Collisional activation experiments performed with these ions indicated that they possess a cyclic structure 49170. The successful neutralization... 

These results from collisional activation experiments have been augmented by ab initio calculations [MP2/6-311 G(df) CCSD(T) level] on the neutral and cationic [Si2,02] surface196,214. The theoretical results point to the existence of three low-lying cationic isomers 60, 61 and 62. 

In neutralization-reionization mass spectrometric experiments on CH2Si+ formed by electron-impact dissociative ionization of ClCH2SiH3, Srinivas, Stilzle and Schwarz found evidence for the formation of a viable neutral molecule whose fragmentation pattern and collisional activation mass spectrum were in accord with a H2C=Si structure422. These authors suggested that their experiments supported electron-capture by CH2Si+" as a mechanism for the formation of H2C=Si in interstellar space. Various models have predicted that H2C=Si is one of the most abundant forms of silicon in dense interstellar clouds423. 

The basic NR mass spectrum contains information on the fraction of undissociated (survivor) ions and also allows one to identify dissociation products that are formed by purely unimolecular reactions. NRMS thus provides information on the intrinsic properties of isolated transient molecules that are not affected by interactions with solvent, matrix, surfaces, trace impurities, radical quenchers, etc. However, because collisional ionization is accompanied by ion excitation and dissociation, the products of neutral and post-reionization dissociations overlap in the NR mass spectra. Several methods have been developed to distinguish neutral and ion dissociations and to characterize further short lived neutral intermediates in the fast beam. Moreover, collisionally activated dissociation (CAD) spectra have been used to characterize the ions produced by collisional reionization of transient neutral intermediates [51]. This NR-CAD analysis adds another dimension to the characterization of neutral intermediates, because it allows one to uncover isomerizations that do not result in a change of mass and thus are not apparent from NR mass spectra alone. 

Dihydroxysulfane, 17, is another elusive acid that has been generated by NRMS [78].The precursor cation-radical, 17+, was obtained by dissociative ionization of dimethylsulfate according to Scheme 6. Upon NR, acid 17 gave an abundant survivor ion showing that the intermediate sulfane was a stable molecule. Collisional activation of neutral 17 caused only minor dissociation by elimination of water, further attesting to the considerable stability of the isolated molecule. 

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