Large Molecule Fragmentation Dynamics Using Delayed Extraction Time-of-Flight Mass Spectroscopy

A time-of-flight mass spectrometer with a pulsed electron beam, delayed and pulsed extraction of the recoil ion is reported. This new technique is named as Delayed Extraction Time of Flight Mass Spectrometer (DEToF). The effectiveness of this technique is highlighted by studying the statistical decay of mono-cations over microsecond timescales from large molecules. Various details of the design and operation are performed in the context of electron impact ionization and fragmentation of few PAHs, naphthalene ( C 10 H 8 ), quinoline ( C 9 H 8 N ) and it isomer Isoquinoline ( C 9 H 8 N ) and are used as a test bench mark for large molecules fragmentation dynamics using DEToF. In this chapter we discuss the fragmentation dynamics of Naphthalene molecule and time evolution of various fragmentation channels of these PAH, explored using a rapid but delayed extraction of recoil ions. The temporal behavior of acetylene ( C 2 H 2 ), HCN, diacetylene ( C 4 H 2 ) and C 2 H 2 +HCN loss are observed and compared with the associated Arrhenius decay constant, internal energy and plasmon excitation energy

Ultraslow radiative cooling of Cn-(n = 3–5)

Ultraslow radiative cooling lifetimes and adiabatic detachment energies for three astrochemically relevant anions, C−n (n = 3–5), are measured using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) infrastructure at Stockholm University. DESIREE maintains a background pressure of ≈10−14 mbar and temperature of ≈13 K, allowing storage of mass-selected ions for hours and providing conditions coined a “molecular cloud in a box.” Here, we construct two-dimensional (2D) photodetachment spectra for the target anions by recording photodetachment signal as a function of irradiation wavelength and ion storage time (seconds to minute time scale). Ion cooling lifetimes, which are associated with infrared radiative emission, are extracted from the 2D photodetachment spectrum for each ion by tracking the disappearance of vibrational hot-band signal with ion storage time, giving 1e cooling lifetimes of 3.1 ± 0.1 s (C−3), 6.8 ± 0.5 s (C−4), and 24 ± 5 s (C−5). Fits of the photodetachment spectra for cold ions, i.e., those stored for at least 30 s, provide adiabatic detachment energies in good agreement with values from laser photoelectron spectroscopy on jet-cooled anions, confirming that radiative cooling has occurred in DESIREE. Ion cooling lifetimes are simulated using a simple harmonic cascade model, finding good agreement with experiment and providing a mode-by-mode understanding of the radiative cooling properties. The 2D photodetachment strategy and radiative cooling modeling developed in this study could be applied to investigate the ultraslow cooling dynamics of a wide range of molecular anions

Cryogenic merged-ion-beam experiments in DESIREE : Final-state-resolved mutual neutralization of Li+ and D-

We have developed an experimental technique to study charge-and energy-flow processes in sub-eV collisions between oppositely charged, internally cold, ions of atoms, molecules, and clusters. Two ion beams are stored in separate rings of the cryogenic ion-beam storage facility DESIREE, and merged in a common straight section where a set of biased drift tubes is used to control the center-of-mass collision energy locally in fine steps. Here, we present measurements on mutual neutralization between Li+ and D- where a time-sensitive imaging-detector system is used to measure the three-dimensional distance between the neutral Li and D atoms as they reach the detector. This scheme allows for direct measurements of kinetic-energy releases, and here it reveals separate populations of the 3s state and the (3p + 3d) states in neutral Li while the D atom is left in its ground state 1s. The branching fraction of the 3s final state is measured to be 57.8 +/- 0.7% at a center-of-mass collision energy of 78 +/- 13 meV. The technique paves the way for studies of charge-, energy-, and mass-transfer reactions in single collisions involving molecular and cluster ions in well-defined quantum states

High-precision electron affinity of oxygen

Negative ions are important in many areas of science and technology, e.g., in interstellar chemistry, for accelerator-based radionuclide dating, and in anti-matter research. They are unique quantum systems where electron-correlation effects govern their properties. Atomic anions are loosely bound systems, which with very few exceptions lack optically allowed transitions. This limits prospects for high-resolution spectroscopy, and related negative-ion detection methods. Here, we present a method to measure negative ion binding energies with an order of magnitude higher precision than what has been possible before. By laser-manipulation of quantum-state populations, we are able to strongly reduce the background from photodetachment of excited states using a cryogenic electrostatic ion-beam storage ring where keV ion beams can circulate for up to hours. The method is applicable to negative ions in general and here we report an electron affinity of 1.461 112 972(87) eV for O-16. High-precision measurements are useful to find isotopic shifts and electron correlation. Here the authors measure electron affinity and hyperfine splitting of atomic oxygen with higher precision than previous studies