Valerio Pirronello - Academia.edu (original) (raw)
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Papers by Valerio Pirronello
Astrophysics and Space Science, 1984
ABSTRACT
Astrophysics and Space Science Library, 1989
A Monte Carlo simulation is presented of the synthesis of H2 in the icy mantles of interstellar g... more A Monte Carlo simulation is presented of the synthesis of H2 in the icy mantles of interstellar grains by the recombination of radicals resulting from the impingement of cosmic ray ions. Grains with a radius of 3300 A seem to enrich the cloud more efficiently that those with radius of 800 A. Past research aimed at understanding the formation of H2 is reviewed.
Nato Advanced Science Institutes Series C, 1991
Sfchem 2002 Chemistry As a Diagnostic of Star Formation, 2003
ABSTRACT
Astronomy and Astrophysics, Mar 30, 1999
Measurements of molecular hydrogen formation on an amorphous carbon sample have been carried out ... more Measurements of molecular hydrogen formation on an amorphous carbon sample have been carried out under astrophysically relevant conditions, i.e., using low fluxes of cold ( ~ 200 K) hydrogen-isotope beams, sample temperature between 5 K and 20 K. The experiments were conducted using the same methods as the ones employed for similar measurements on an olivine sample; therefore, results from the two experiments can be compared to each other. As in the case for the study of hydrogen recombination on a silicate surface, we find that mobility of hydrogen is thermally activated. However, differently from the olivine case, the activation energy for the overall process of diffusion and desorption is significantly higher, and the recombination efficiency, at similar total fluence of impinging atoms and sample temperature during irradiation, is also higher. Implications of these measurements for astrophysical environments are discussed. Research supported in part by NASA under grants no.\ NAG5-4998 and NAG5-6822.
Astronomy and Astrophysics, Jan 30, 1983
Recent experimental evidences on the H2 production by keV ions bombardment of H2O frozen gas are ... more Recent experimental evidences on the H2 production by keV ions bombardment of H2O frozen gas are briefly summarized. The possibility of H2 production via such a process in comets as a function of their temperature (or distance to the Sun) is discussed.
Astron Astrophys, 1981
ABSTRACT
The Astrophysical Journal, Jun 29, 1989
Chemical modifications induced by cosmic-ray irradiation in cometary nuclei are evaluated. The pr... more Chemical modifications induced by cosmic-ray irradiation in cometary nuclei are evaluated. The production of formaldehyde via this mechanism is estimated at various depths in the nucleus of a long-period comet (T about 1 million yr). The abundance of H2CO and of its photodissociation product HCO in the coma of such a comet when it approaches the sun is also computed and can be used to check observationally the validity of the low-energy cosmic-ray flux used in the calculations. In particular, on the basis of calculations and of observations of complex molecules, synthesized by particle bombardment, it will be possible to evaluate whether the so-called 'anomalous component' of cosmic rays has an interstellar origin or not.
We are going to present the results of a recent experimental study of the formation of molecular ... more We are going to present the results of a recent experimental study of the formation of molecular hydrogen on amorphous silicate grains under interstellar (ISM) conditions. The data obtained from TPD (Temperature Programmed Desorption) experiments are analyzed using a rate equation model. The energy barriers for the relevant diffusion and desorption processes are obtained. The results show they are significantly higher than those obtained for polycrystalline silicates, indicating the importance of different morphologies. Based on the value of these barriers, we evaluated the efficiency of molecular hydrogen formation. It is found that the most efficient formation is happening in a temperature domain that is relevant to diffuse interstellar clouds. This shows that amorphous silicates are good candidates of interstellar grains and are efficient catalysts of molecular hydrogen formation. This work was supported by NASA through Grants NAG5-9093, NAG5-11438, NASA 1284471, NNG06GD84G, and NSF AST-0507405 (G.V.), by the Israel Science Foundation and the Adler Foundation for Space Research (O.B.), and by the Italian Ministry for University and Scientific Research through Grant 21043088 (V.P.)
Proceedings of the International Astronomical Union, 2011
We investigated neutral radical-molecule reactions CO + OH without external energy inputs to inve... more We investigated neutral radical-molecule reactions CO + OH without external energy inputs to investigate possible CO2 formation pathways inside dense molecular clouds, where UV field is relatively weak. OH radicals were produced by dissociating H2O in microwave-induced plasma and cooled down to 100 K before they were codeposited with CO on a cold Al surface at 10-40 K. Reaction products were monitored in-situ by FTIR spectroscopy. We observed the formation of CO2 in the reaction products. Furthermore, formation of trans- and cis-HOCO radicals were also identified. On this basis, we consider CO2 was formed by the following reactions on the cold Al surface: CO + OH → cis-HOCO → trans-HOCO → CO_2 + H, which have been proposed for the CO2 formation route in the gas phase. Our results suggest that the above reactions have little or no activation barrier. Conversion factor of CO to CO2 was up to 10 {%} under the present experimental conditions. In addition to CO2 and HOCO radicals, we found that carbonic acid, H2CO3, was formed probably by the following reactions: HOCO + OH → H_2CO_3 H2CO3 has never been found in molecular clouds. However, if H2CO3 really exists in interstellar ices, it may act as an acid molecule to react with base molecules such as NH3, which results in the formation of NH4+, one of the possible candidates for the unidentified 6.8 μ m band observed toward various astronomical sources. Furthermore, we propose that H2CO3 itself could have a contribution to 6.8 μ m band.
H2 in Space, 1999
... By using H atoms in one lino and D atoms in the other, we can look at the formation of HD on ... more ... By using H atoms in one lino and D atoms in the other, we can look at the formation of HD on the surface, knowing that there are no other spurious sources of HD. ... Phys. 85, 1131. Rettner, CT, Michelsen, HA & Auerbach, DJ 1995 J. Chem. Phys. 102, 4625. ...
Il Nuovo Cimento B, 1978
The interaction of a gravitational wave with a dissipative fluid is studied in the high-frequency... more The interaction of a gravitational wave with a dissipative fluid is studied in the high-frequency approximation. The gauge invariance and the degrees of freedom of the gravitational wave in the matter have been carefully examined.
34Th Cospar Scientific Assembly, 2002
ABSTRACT
Astrophysics and Space Science, 1984
ABSTRACT
Astrophysics and Space Science Library, 1989
A Monte Carlo simulation is presented of the synthesis of H2 in the icy mantles of interstellar g... more A Monte Carlo simulation is presented of the synthesis of H2 in the icy mantles of interstellar grains by the recombination of radicals resulting from the impingement of cosmic ray ions. Grains with a radius of 3300 A seem to enrich the cloud more efficiently that those with radius of 800 A. Past research aimed at understanding the formation of H2 is reviewed.
Nato Advanced Science Institutes Series C, 1991
Sfchem 2002 Chemistry As a Diagnostic of Star Formation, 2003
ABSTRACT
Astronomy and Astrophysics, Mar 30, 1999
Measurements of molecular hydrogen formation on an amorphous carbon sample have been carried out ... more Measurements of molecular hydrogen formation on an amorphous carbon sample have been carried out under astrophysically relevant conditions, i.e., using low fluxes of cold ( ~ 200 K) hydrogen-isotope beams, sample temperature between 5 K and 20 K. The experiments were conducted using the same methods as the ones employed for similar measurements on an olivine sample; therefore, results from the two experiments can be compared to each other. As in the case for the study of hydrogen recombination on a silicate surface, we find that mobility of hydrogen is thermally activated. However, differently from the olivine case, the activation energy for the overall process of diffusion and desorption is significantly higher, and the recombination efficiency, at similar total fluence of impinging atoms and sample temperature during irradiation, is also higher. Implications of these measurements for astrophysical environments are discussed. Research supported in part by NASA under grants no.\ NAG5-4998 and NAG5-6822.
Astronomy and Astrophysics, Jan 30, 1983
Recent experimental evidences on the H2 production by keV ions bombardment of H2O frozen gas are ... more Recent experimental evidences on the H2 production by keV ions bombardment of H2O frozen gas are briefly summarized. The possibility of H2 production via such a process in comets as a function of their temperature (or distance to the Sun) is discussed.
Astron Astrophys, 1981
ABSTRACT
The Astrophysical Journal, Jun 29, 1989
Chemical modifications induced by cosmic-ray irradiation in cometary nuclei are evaluated. The pr... more Chemical modifications induced by cosmic-ray irradiation in cometary nuclei are evaluated. The production of formaldehyde via this mechanism is estimated at various depths in the nucleus of a long-period comet (T about 1 million yr). The abundance of H2CO and of its photodissociation product HCO in the coma of such a comet when it approaches the sun is also computed and can be used to check observationally the validity of the low-energy cosmic-ray flux used in the calculations. In particular, on the basis of calculations and of observations of complex molecules, synthesized by particle bombardment, it will be possible to evaluate whether the so-called 'anomalous component' of cosmic rays has an interstellar origin or not.
We are going to present the results of a recent experimental study of the formation of molecular ... more We are going to present the results of a recent experimental study of the formation of molecular hydrogen on amorphous silicate grains under interstellar (ISM) conditions. The data obtained from TPD (Temperature Programmed Desorption) experiments are analyzed using a rate equation model. The energy barriers for the relevant diffusion and desorption processes are obtained. The results show they are significantly higher than those obtained for polycrystalline silicates, indicating the importance of different morphologies. Based on the value of these barriers, we evaluated the efficiency of molecular hydrogen formation. It is found that the most efficient formation is happening in a temperature domain that is relevant to diffuse interstellar clouds. This shows that amorphous silicates are good candidates of interstellar grains and are efficient catalysts of molecular hydrogen formation. This work was supported by NASA through Grants NAG5-9093, NAG5-11438, NASA 1284471, NNG06GD84G, and NSF AST-0507405 (G.V.), by the Israel Science Foundation and the Adler Foundation for Space Research (O.B.), and by the Italian Ministry for University and Scientific Research through Grant 21043088 (V.P.)
Proceedings of the International Astronomical Union, 2011
We investigated neutral radical-molecule reactions CO + OH without external energy inputs to inve... more We investigated neutral radical-molecule reactions CO + OH without external energy inputs to investigate possible CO2 formation pathways inside dense molecular clouds, where UV field is relatively weak. OH radicals were produced by dissociating H2O in microwave-induced plasma and cooled down to 100 K before they were codeposited with CO on a cold Al surface at 10-40 K. Reaction products were monitored in-situ by FTIR spectroscopy. We observed the formation of CO2 in the reaction products. Furthermore, formation of trans- and cis-HOCO radicals were also identified. On this basis, we consider CO2 was formed by the following reactions on the cold Al surface: CO + OH → cis-HOCO → trans-HOCO → CO_2 + H, which have been proposed for the CO2 formation route in the gas phase. Our results suggest that the above reactions have little or no activation barrier. Conversion factor of CO to CO2 was up to 10 {%} under the present experimental conditions. In addition to CO2 and HOCO radicals, we found that carbonic acid, H2CO3, was formed probably by the following reactions: HOCO + OH → H_2CO_3 H2CO3 has never been found in molecular clouds. However, if H2CO3 really exists in interstellar ices, it may act as an acid molecule to react with base molecules such as NH3, which results in the formation of NH4+, one of the possible candidates for the unidentified 6.8 μ m band observed toward various astronomical sources. Furthermore, we propose that H2CO3 itself could have a contribution to 6.8 μ m band.
H2 in Space, 1999
... By using H atoms in one lino and D atoms in the other, we can look at the formation of HD on ... more ... By using H atoms in one lino and D atoms in the other, we can look at the formation of HD on the surface, knowing that there are no other spurious sources of HD. ... Phys. 85, 1131. Rettner, CT, Michelsen, HA & Auerbach, DJ 1995 J. Chem. Phys. 102, 4625. ...
Il Nuovo Cimento B, 1978
The interaction of a gravitational wave with a dissipative fluid is studied in the high-frequency... more The interaction of a gravitational wave with a dissipative fluid is studied in the high-frequency approximation. The gauge invariance and the degrees of freedom of the gravitational wave in the matter have been carefully examined.
34Th Cospar Scientific Assembly, 2002
ABSTRACT