14 research outputs found
Two-Photon Doppler cooling of alkaline-earth-metal and ytterbium atoms
A new possibility of laser cooling of alkaline-earth-metal and Ytterbium
atoms using a two-photon transition is analyzed. We consider a -
transition, with excitation in near resonance with the
level. This greatly increases the two-photon transition rate, allowing an
effective transfer of momentum. The experimental implementation of this
technique is discussed and we show that for Calcium, for example, two-photon
cooling can be used to achieve a Doppler limit of 123 microKelvin. The
efficiency of this cooling scheme and the main loss mechanisms are analyzed.Comment: 7 pages, 5 figure
Photoabsorption and photoionization studies of the amino acid proline in the VUV region
Ionic fragmentation of the sublimated amino acid DL-proline has been studied using time-of-flight mass spectrometry and synchrotron radiation. Total ion yield and mass spectra were recorded in the 13 to 21.6 eV energy range. Partial ion yields have been calculated for the produced fragments and the results analyzed in a comparative way. Mass spectrum of proline previously obtained at 21.21 eV using photons from a discharge lamp (He I), was used as reference in the comparison to the synchrotron radiation based spectra. The loss of the COOH fragment represents the most probable dissociation pathway following the photoionization of DL-proline in the valence region. These are the first results of total and partial ion yields spectra for this molecule in its gas phase in the valence region using time-of-flight spectrometry
Photostability of gas- and solid-phase biomolecules within dense molecular clouds due to soft X-rays
An experimental photochemistry study involving gas- and solid-phase amino
acids (glycine, DL-valine, DL-proline) and nucleobases (adenine and uracil)
under soft X-rays was performed. The aim was to test the molecular stabilities
of essential biomolecules against ionizing photon fields inside dense molecular
clouds and protostellar disks analogs. In these environments, the main energy
sources are the cosmic rays and soft X-rays. The measurements were taken at the
Brazilian Synchrotron Light Laboratory (LNLS), employing 150 eV photons.
In-situ sample analysis was performed by Time-of-flight mass spectrometer
(TOF-MS) and Fourier transform infrared (FTIR) spectrometer, for gas- and
solid- phase analysis, respectively. The half-life of solid phase amino acids,
assumed to be present at grain mantles, is at least 3E5 years and 3E8 years
inside dense molecular clouds and protoplanetary disks, respectively. We
estimate that for gas-phase compounds these values increase one order of
magnitude since the dissociation cross section of glycine is lower at gas-phase
than at solid phase for the same photon energy. The half-life of solid phase
nucleobases is about 2-3 orders of magnitude higher than found for amino acids.
The results indicate that nucleobases are much more resistant to ionizing
radiation than amino acids. We consider these implications for the survival and
transfer of biomolecules in space environments.Comment: 10 pages, 5 figures, 2 tables. Accepted to be published in MNRA
Anionic and Cationic Photodissociation of the Chloroform Molecule Excited in the Vicinity of the Cl 1s Edge
The anionic and cationic photodissociation from deep-core excited chloroform molecule has been investigated in the vicinity of the Cl 1s excitation edge. We used synchrotron radiation, time of flight mass spectrometry and ion yield spectroscopy. From our partial anion yield results we were able to observe for the first time the formation of the following anionic species: Cl-, H- and C-. From our TOF spectra we determined the cations produced in order to discuss the photoionization and dissociation dynamics for this core excited molecule. It provided evidences of the complex dynamics of negative and positive ion formation from CHCl3 upon photo-excitation in the vicinity of the Cl 1s edge
Valence and Inner Electronic Excitation, Ionization, and Fragmentation of Perfluoropropionic Acid
The
photoexcitation, photoionization, and photofragmentation of
gaseous CF<sub>3</sub>CF<sub>2</sub>CÂ(O)ÂOH were studied by means of
synchrotron radiation in the valence and inner energy regions. Photofragmentation
events were detected from 11.7 eV through formation of COH<sup>+</sup>, C<sub>2</sub>F<sub>4</sub><sup>+</sup>, and the parent species
M<sup>+</sup>. Because the vertical ionization potential has been
reported at 11.94 eV, the starting energy used in this study, 11.7
eV, falls just inside of the tail of the ionization band in the photoelectron
spectra. Information from the total ion yield spectra around the C
1s, O 1s, and F 1s ionization potentials allows the energies at which
different resonance transitions take place in the molecule to be determined.
These transitions have been assigned by comparison with the results
of the analysis of similar compounds. In the inner energy region,
both kinetic energy release (KER) values and the slope and shape of
double coincidence islands obtained from photoelectronâphotoionâphotoion
coincidence (PEPIPICO) spectra allow different photofragmentation
mechanisms to be elucidated
Photoexcitation, Photoionization, and Photofragmentantion of CF<sub>3</sub>CF<sub>2</sub>CF<sub>2</sub>C(O)Cl Using Synchrotron Radiation between 13 and 720 eV
The main inner shell ionization edges
of gaseous CF<sub>3</sub>CF<sub>2</sub>CF<sub>2</sub>CÂ(O)ÂCl, including
Cl 2p, C 1s, O 1s,
and F 1s, have been measured in Total Ion Yield (TIY) mode by using
tunable synchrotron radiation, and several resonance transitions have
been assigned with the help of quantum chemical calculations. Interestingly,
resonance transitions observed in the C 1s region can be assigned
to different carbon atoms in the molecule according to the degree
of fluorine substitution. Ionic photofragmentation processes have
been studied by time-of-flight mass spectrometry in the Photoelectron-Photoion-Coincidence
(PEPICO) and Photoelectron-Photoion-Photoion-Coincidence (PEPIPICO)
modes. These techniques revealed a âmemory-lostâ effect
especially around the C 1s region, since the fragmentation events
are independent of the energy range considered. Moreover, different
fragmentation mechanisms were inferred from these spectra in the valence
(13.0â21.0 eV) as well as in the inner (180.0â750.0
eV) electronic energy regions. The vibrational spectral features of
CF<sub>3</sub>CF<sub>2</sub>CF<sub>2</sub>CÂ(O)Cl have been interpreted
in terms of a conformational equilibrium between two conformations
(<i>gauche</i> and <i>anti</i> of the CC single
bond with respect to the CCl one) at room temperature, as determined
from quantum chemical calculations and the detailed analysis of the
infrared spectrum