Collisionally induced

Metastable ions yield valuable information on fragmentation in mass spectrometry, providing insight into molecular structure. In electron ionization, metastable ions appear naturally along with the much more abundant normal ions. Abundances of metastable ions can be enhanced by collisionally induced decomposition. 

A constant-mass-difference scan. Source ions (m, f,. .., fj) are passed successively by Q1 into Q2, where collisionally induced dissociation occurs. Q3 is set to pass only those ions produced in Q2 that have a predetermined mass difference (Am) between the ions passed by Ql. In this example, they are m, - f, (= Am) and f, - fj (= Am), so, although all ions pass into Q2, only f, f, have a mass difference (Am) equal to that selected for Q3. 

Metastable and collisionally induced fragment ions can be detected efficiently by a triple quadrupole instmment. By linking the scanning regions of the first and third quadrupoles, important information about molecular structure is easily obtained. 

Collision of normal ions from the first quadrupole with gas molecules in the second quadrupole increases fragmentation, a process known as either collisionally induced dissociation (CID) or collisionally activated decomposition (CAD). 

PCI, positive chemical ionisation El, electron impact CID, collisionally induced dissociation. 

Collisional deactivation. Collisions with other molecules can stimulate the relaxation to the ground state. There are no selection rules for collisionally induced transitions. 

Fragmentation Region metastable decay collisional induced dissociation photodissociation... 

The fluoresence lifetimes calculated for TIN in low viscosity alcohols are approximately proportional to the solvent viscosity (12) which suggests that in these solvents there is a non-radiative process related to. the rotational diffusion mobility of the TIN molecule. The observed extent of the quenching, however, is significantly greater than that expected due to viscosity effects alone and cannot be explained by a collisionally-induced, Stern-Volmer type process involving methanol molecules (25.) as the appropriate plot is non-linear. 

Burgers, P.C. Holmes, J.E. Mommers, A.A. Terlouw, J.K. Neutral Products of Ion Fragmentations Hydrogen Cyanide and Hydrogen Isocyanide (HNC) Identified by Collisionally Induced Dissociative Ionization. Chem. Phys. Lett. 1983,102,1-3. 

The effects of such collisionally induced kicks are treated within the so-called pressure broadening (sometimes called collisional broadening) model by modifying the free-rotation correlation function through the introduction of an exponential damping factor exp( -Itl/x) ... 

Since both ESP and ISP produce quasimolecular ions, more sophisticated techniques, such as LC-MS-MS are required to obtain diagnostic fragment ions and, thus, analyte structure elucidation (117, 118). Identification can often be achieved by using daughter ion MS-MS scans and collisionally induced dissociation (CID), most commonly on a triple quadrupole MS in this way, dissociation of the quasimolecular ion occurs and diagnostic structural information can be obtained (119). 

Anastassiou has provided very strong evidence for collisionally induced relaxation of singlet cyanonitrene to its triplet ground state.67 Thermolysis of cyanogen azide at 40-45° in cis- or trans-1,2-dimethyl-... 

Collisionally induced intersystem crossing from CN(/I2n - ) observed at low pressures... 

Ashfold and Simons (47a) have recently shown that both CN(/l2ri) and (B E+) states are formed in the vacuum ultraviolet photolysis of BrCN. At the low pressure limit CN(B3 + ) shows a vibrational population inversion at the 1236 A photolysis (a maximum at o = 2), while at higher pressures the population shows a monotonic decrease with an increase of o observed before by Mole and Okabe (692). They attribute the pressure elTect to the collisionally induced inicrsystcm crossing between the /t2Il (o > 10) and neighboring B2Z + (o > 0) levels. Because of the long radiative life of A2n sialc ( - 7 /isec) (532), it is susceptible to collisions even at a pressure of 10 mtorr. 

Both the B, and 3fl, states induce isomerization of cis-2-butene to trrms-2-butene (273). m-2-Butene is very efficient in collisionally inducing a B, B, transition. 

Collisionally induced emission S( S)- S( D) has been found to be a major path for deactivation of S( S) atoms by rare gases and by N2 [Black et al. (116)] in analogy with O( S) atoms described in Section 1V-4.2. 

There are three methods which have been used to study collisions of Rydberg atoms with neutrals. They are direct measurement of collisionally induced population changes, line shift and broadening measurements, and photon echo measurements.23 In this chapter we describe the first of these. The last two are described in the chapter immediately following. 

Fig. 11.7 Collisionally induced diabatic ionization features observed following collisions of laser-excited Xe 31f atoms with Xe target gas at a pressure of 1(T5 Torr for 8 fis in the presence of several applied static fields. The arrows indicate the ranges of ionizing field strengths over which n = 30 and 31 states are expected to ionize diabatically (from ref. 43).

Because of the importance of the biphenyl scaffold, as a structure of pharmaceutical and active therapeutic compounds, the mass spectrometric behavior of a series of 6,6-disubstituted dibenzo[r//][l,3]dioxepins 36 has been studied. The electron ionization-induced fragmentation patterns were discussed based on use of labeled compounds, accurate mass measurements, and collisionally induced dissociation experiments using an ion trap <2006JMP577>. 

Fast Atom Bombardment Combined with Tandem Mass Spectrometry for the Study of Collisionally Induced Remote Charge Site Decompositions... 

E. Yoon and R. A. Laine, Linkage position determination in a novel set of permethylated neutral trisaccharides by collisional-induced dissociation and tandem mass spectrometry. Biol. Mass Spectrom., 21 (1992) 479-485. 

Snider is best known for his paper reporting what is now referred to as the Waldmann-Snider equation.34 (L. Waldmann independently derived the same result via an alternative method.) The novelty of this equation is that it takes into account the consequences of the superposition of quantum wavefunctions. For example, while the usual Boltzmann equation describes the collisionally induced decay of the rotational state probability distribution of a spin system to equilibrium, the modifications allow the effects of magnetic field precession to be simultaneously taken into account. Snider has used this equation to explain a variety of effects including the Senftleben-Beenakker effect (i.e., is, the magnetic and electric field dependence of gas transport coefficients), gas phase NMR relaxation, and gas phase muon spin relaxation.35... 

High-throughput bioanalysis screening approaches involve the characterization of full-scan mass spectra and MS/MS properties to determine the predominant molecular and product ions, respectively. This information is useful for the selection of appropriate ions for selected reaction monitoring (SRM) experiments. Settings such as collision energies and collisionally induced dissociation (CID) pressure or gas thickness can be optimized as well. Typically, the most abundant product ion is selected for SRM. Various acquisition software programs are used to perform the experiment, display the results, and process the data in an automated fashion. 

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