| 1. |
- Bull, James N., et al.
(författare)
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Photodetachment and photoreactions of substituted naphthalene anions in a tandem ion mobility spectrometer
- 2019
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 217, s. 34-46
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Tidskriftsartikel (refereegranskat)abstract
- Substituted naphthalene anions (deprotonated 2-naphthol and 6-hydroxy-2-naphthoic acid) are spectroscopically probed in a tandem drift tube ion mobility spectrometer (IMS). Target anions are selected according to their drift speed through nitrogen buffer gas in the first IMS stage before being exposed to a pulse of tunable light that induces either photodissociation or electron photodetachment, which is conveniently monitored by scavenging the detached electrons with trace SF6 in the buffer gas. The photodetachment action spectrum of the 2-naphtholate anion exhibits a band system spanning 380-460 nm with a prominent series of peaks spaced by 440 cm(-1), commencing at 458.5 nm, and a set of weaker peaks near the electron detachment threshold corresponding to transitions to dipole-bound states. The two deprotomers of 6-hydroxy-2-naphthoic acid are separated and spectroscopically probed independently. The molecular anion formed from deprotonation of the hydroxy group gives rise to a photodetachment action spectrum similar to that of the 2-naphtholate anion with an onset at 470 nm and a maximum at 420 nm. Near the threshold, the photoreaction with SF6 is observed with displacement of an OH group by an F atom. In contrast, the anion formed from deprotonation of the carboxylic acid group gives rise to a photodissociation action spectrum, recorded on the CO2 loss channel, lying at much shorter wavelengths with an onset at 360 nm and maximum photoresponse at 325 nm.
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| 2. |
- Bull, James N., et al.
(författare)
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Ultraslow radiative cooling of Cn- (n=3-5)
- 2019
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:11
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Tidskriftsartikel (refereegranskat)abstract
- Ultraslow radiative cooling lifetimes and adiabatic detachment energies for three astrochemically relevant anions, Cn- (n = 3-5), are measured using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) infrastructure at Stockholm University. DESIREE maintains a background pressure of approximate to 10(-14) mbar and temperature of approximate to 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 (C3-), 6.8 +/- 0.5 s (C4-), and 24 +/- 5 s (C5-). 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.
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| 3. |
- Giacomozzi, Linda, et al.
(författare)
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Decay pathways for protonated and deprotonated adenine molecules
- 2019
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:4
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Tidskriftsartikel (refereegranskat)abstract
- We have measured fragment mass spectra and total destruction cross sections for protonated and deprotonated adenine following collisions with He at center-of-mass energies in the 20-240 eV range. Classical and ab initio molecular dynamics simulations are used to provide detailed information on the fragmentation pathways and suggest a range of alternative routes compared to those reported in earlier studies. These new pathways involve, for instance, losses of HNC molecules from protonated adenine and losses of NH2 or C3H2N2 from deprotonated adenine. The present results may be important to advance the understanding of how biomolecules may be formed and processed in various astrophysical environments.
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| 4. |
- Kjaer, Christina, et al.
(författare)
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Luminescence Spectroscopy of Rhodamine Homodimer Dications in Vacuo Reveals Strong Dye-Dye Interactions
- 2019
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Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 20:4, s. 533-537
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Tidskriftsartikel (refereegranskat)abstract
- Being alone or together makes a difference for the photophysics of dyes but for ionic dyes it is difficult to quantify the interactions due to solvent screening and nearby counter ions. Gas-phase luminescence experiments are desirable and now possible based on recent developments in mass spectrometry. Here we present results on tailor-made rhodamine homodimers where two dye cations are separated by methylene linkers, (CH2)(n). In solution the fluorescence is almost identical to that from the monomer whereas the emission from bare cation dimers redshifts with decreasing n. In the absence of screening, the electric field from the charge on one dye is strong enough to polarize the other dye, both in the ground state and in the excited state. An electrostatic model based on symmetric dye responses (equal induced-dipole moments in ground state) captures the underlying physics and demonstrates interaction even at large distances. Our results have possible implications for gas-phase Forster Resonance Energy Transfer.
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| 5. |
- Stockett, Mark H., et al.
(författare)
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Storage time dependent photodissociation action spectroscopy of polycyclic aromatic hydrocarbon cations in the cryogenic electrostatic storage ring DESIREE
- 2019
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 217, s. 126-137
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Tidskriftsartikel (refereegranskat)abstract
- The multi-photon photodissociation action spectrum of the coronene cation (C24H12+) has been measured in the cryogenic electrostatic storage ring DESIREE (Double ElectroStatic Ion Ring ExpEriment) as a function of storage time. These measurements reveal not only the intrinsic absorption profile of isolated coronene cations, but also the rate at which hot-band absorptions are quenched by radiative cooling. Just after injection, the action spectrum is severely reddened by hot-band absorptions. These hot bands fade with a time constant of 200 ms, which is consistent with radiative cooling via infrared emission from vibrational transitions. A comparison of the present results to those obtained in cryogenic ion trap experiments is discussed at length.
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