9 research outputs found
Cascade infrared thermal photon emission
The time development of the excitation energy of molecules and clusters
cooling by emission of thermal vibrational infrared radiation has been studied.
The energy distributions and the photon emission rates develop into
near-universal functions that can be characterized with only a few parameters,
irrespective of the precise vibrational spectra and oscillator strengths of the
systems. The photon emission constant and emitted power averaged over all
thermally populated states vary linearly with total excitation energy with a
small offset. The time developments of ensemble internal energy distributions
are calculated with respect to their first two moments. For the derived linear
dependence of the emission rate constant, these results are exact
Velocity Map Imaging with No Spherical Aberrations
Velocity map imaging (VMI) is a powerful technique that allows to infer the
kinetic energy of ions or electrons that are produced from a large volume in
space with good resolution. The size of the acceptance volume is determined by
the spherical aberrations of the ion optical system. Here we present an
analytical derivation for velocity map imaging with no spherical aberrations.
We will discuss a particular example for the implementation of the technique
that allows using the reaction microscope recently installed in the Cryogenic
storage ring (CSR) in a VMI mode. SIMION simulations confirm that a beam of
electrons produced almost over the entire volume of the source region, with
width of 8 cm, can be focused to a spot of 0.1 mm on the detector. The use of
the same formalism for position imaging, as well as an option of position
imaging in one axis and velocity map imaging in a different axis, are also
discussed
Peptide bond formation in the protonated serine dimer following vacuum UV photon-induced excitation
Possible routes for intra-cluster bond formation (ICBF) in protonated serine dimers have been studied. We found no evidence of ICBF following low energy collision-induced dissociation (in correspondence with previous works), however, we do observe clear evidence for ICBF following photon absorption in the 4.6–14 eV range. Moreover, the comparison of photon-induced dissociation measurements of the protonated serine dimer to those of a protonated serine dipeptide provides evidence that ICBF, in this case, involves peptide bond formation (PBF). The experimental results are supported by ab initio molecular dynamics and exploration of several excited state potential energy surfaces, unraveling a pathway for PBF following photon absorption. The combination of experiments and theory provides insight into the PBF mechanisms in clusters of amino acids, and reveals the importance of electronic excited states reached upon UV/VUV light excitatio
Effect of a localized charge on the stability of Van der Waals clusters
The stability of anionic (SF6)-N clusters (in the range of N< 23), generated in a
supersonic expansion ion source with electron impact ionization, was investigated by
measuring their blackbody induced radiative dissociation (BIRD) rates in an electrostatic
ion beam trap (EIBT) at room temperature. The lifetime traces of EIBT-stored clusters were
subjected to “master equation analysis” and the activation energies, Ea, for the evaporation
of a SF6 monomer were
extracted. We find that the decay rates of (SF6)-N anionic clusters are larger than those of cationic SF+5(SF6)N-1 measured previously by the same method, and their
corresponding activation energies to be smaller. These observations provide further
insight into the effect of localized charge on cluster stability
Clusters of betaine with positive and negative ions: Evidence for the betaine tetramer being magic
Counterion-controlled spectral tuning of the protonated Schiff-base retinal
Color vision is based on the ability of different opsin proteins to tune the absorption band of their chromophore, the retinal protonated Schiff base (RPSB). Two main mechanisms proposed for this tunability are geometric and electrostatic. Here we probe the latter effect experimentally and by a quantum chemical calculation of the absorption by an isolated complex containing the retinal chromophore and molecules with a strong dipole moment. Betaine complexation causes an anomalously large blue shift. The shift provides direct evidence that the strong charge-transfer character of the electronic transition is the cause of the opsin shift, and shows that the electric field of the counterion is responsible for the color tuning, which allows absorption of light in the blue region of the visible spectrum by opsin proteins
Vacuum UV studies of protonated serine clusters
International audienceAbstract In a recent work, we have shown that photon absorption can cause a chemical bond to be created between the two monomers within a protonated serine dimer, a process known as intra-cluster bond formation, despite this process not occurring following thermal excitation via low energy collision-induced dissociation (LE-CID). Here we show further evidence for non-statistical photon-induced dissociation (PID) of the protonated serine dimer. In addition we discuss LE-CID and PID studies of the protonated serine octamer, showing that in this case as well, PID leads to non-statistical fragmentation and to the formation of two bonds between three neighboring monomers