Internal energy distributions of tungsten hexacarbonyl ions after neutralization—Reionization

Abstract

The internal energy distributions P(ε) transferred to W(CO) 6 (+·) during the kiloelectronvolt collisions that occur upon neutralization-reionization (NR) have been estimated based on the relative abundances of the W(CO) 0-6 (+·) products present in NR spectra (thermochemical method). The average internal energy of the incipient {W(CO) 6 (+·) }(*) ions arising after near thermoneutral neutralization with trimethylamine followed by reionization with O2 is ∼9 eV for 8-keV precursor ions and is mainly deposited during reionization, For comparison, the mean internal energy of {W(CO) 6 (+·) }(*) after electron ionization (EO or collisionally activated dissociation (CAD) is ∼ 6 eV. Making the neutralization step endothermic slightly increases the overall excitation gained; however, a large increase in endothermicity (> 16 eV) causes only a modest rise of the average internal energy (<2 eV). The P(ε) curve for NR increases exponentially up to ∼ 6 eV and levels off at higher energies.. showing that the probability of imparting large internal energies (6-17 eV) is high. In sharp contrast, the most probable excitation on CAD is ≤6 eV, and the probability of deposition of larger energies declines exponentially. The mean internal energies after CAD and NR decrease steadily when the kinetic energy is lowered. The structure (minima-maxima) observed in the P(ε) distribution for El, which most likely originates from Franck-Condon factors, is not reproduced in the distributions for NR or high energy CAD, despite the fact that all three methods involve electronic excitation. Because of the large internal energies transferred upon NR, NR mass spectrometry could be particularly useful in the differentiation of ionic isomers with high dissociation but low isomerization thresholds.

Nonergodicity in electron capture dissociation investigated using hydrated ion nanocalorimetry

“…Specifically, if the threshold dissociation energies for a series of consecutive reactions are known, information about the internal energy deposition can be obtained from the distribution of product ions formed. This method, pioneered by Cooks and coworkers [42,43], has been used to characterize the internal energy deposition of several activation methods [43][44][45]. For large clusters, where loss of water molecules is the only process observed, we have shown that the number of water molecules lost from the reduced precursor can be used as a measure of the internal energy deposition in these clusters [62].…”

“…Thus, the ratio of these two ions serve as a measure of the internal energy deposited into this ion [39 -41]. A measure of the internal energy can also be obtained from the abundances of fragment ions formed via consecutive reaction pathways with known critical formation energies [42][43][44][45]. For example, activation of Fe(CO) 5 ϩ· can result in sequential loss of CO molecules with critical energies ranging from 1.15 eV for the loss of the first CO molecule to 7.58 eV for the loss of all five CO molecules; formation of FeC ϩ requires 15.7 eV [43].…”

“…The abundances of the fragment ions formed by activation of Fe(CO) 5 ϩ· or analogous ions provide a measure of the range and magnitude of the internal energy that is deposited into this ion. This method, first demonstrated by Kenttämaa and Cooks [42], has been used to characterize the internal energy distribution resulting from ion-surface and ion-gas collisions [43] as well as other activation methods [44,45]. The effective internal temperature of an ion can also be obtained from measurements of dissociation kinetics if Arrhenius parameters in the rapid energy exchange limit for the dissociation process are known.…”

Neutralization-reionization mass spectrometry applied to organometallic and coordination chemistry (update: 1994-1998)

“…First, the amount of internal energy that can be transferred to the ion and the neutral during the NR process usually exceeds the amount of energy transferred in collisional activation. This observation, for example, has been made for the dissociation of tungsten hexacarbonyl ions (Beranova and Wesdemiotis, 1994). The NR mass spectra of these ions displayed a greater dissociation compared to the CID mass spectra and with the EI ionization of W(CO) 6 .…”

Investigation of Energy Deposited by Femtosecond Electron Transfer in Collisions Using Hydrated Ion Nanocalorimetry

“…For example, the center-of-mass collision energy between a doubly charged cation of mass 200 Da with 100 keV of kinetic energy and a Cs atom is 39.9 keV. A measure of the internal energy deposition into an ion can be obtained using “chemical thermometers”, which are ions that have known dissociation energies and entropies 33-43. Metal carbonyl complexes that have known fragment appearance energies have been used to investigate the internal energy deposition from a variety of activation methods 33-36.…”