Water vapor was excited by a 0.53 MeV pulsed electron beam and examined for luminescence emission... more Water vapor was excited by a 0.53 MeV pulsed electron beam and examined for luminescence emission in the 360–600 nm region. Spectral lines arising from the Balmer transitions H(n=4→n=2), H(n=5→n=2), and H(n=6→n=2) of the hydrogen atom and the transitions 3p4D05/2→3s4P3/2, 3p4D07/2→ 3s4P5/2, and 3p4D01/2→3s4P1/2 of the O+ ion were observed. The Balmer lines were found to be quenched by water vapor with rate constants at 293 K of (9.77±0.26)×10−9, (10.67±0.45)×10−9, and (12.3±2.3)×10−9 cm3 molecule−1 s−1, respectively. The excited O+ ions were also quenched strongly by water vapor but line intensities were insufficient for rate measurements to be carried out.
Journal of Photochemistry and Photobiology, Apr 1, 1984
... 5 TI Quickenden, JA Irvin and DF Sangster, J. Client Plays., 69 (1978) 4395. 6 G. Herzberg, M... more ... 5 TI Quickenden, JA Irvin and DF Sangster, J. Client Plays., 69 (1978) 4395. 6 G. Herzberg, Molecular Spectra and Molecular Structure, Vol. I, The Spectra of Diatomic Molecules, VanNostrand Reinhold, New York, 1966. References. 1. G. Herzberg J. Chem. Phys. ...
S!E;E~T [ 11 hns reported emissions from three upper triplet levels cs: CO, d 3A, e 32: and ZI' 3... more S!E;E~T [ 11 hns reported emissions from three upper triplet levels cs: CO, d 3A, e 32: and ZI' 32, when CCS undergocs collision with xenon atoms excited to the IL, level by the xenon resonance tine at I47 nm. The observed bands arise from transitions to t!le lowest tripfel ievel, a 311. The excited slates are !W high if1 LVIL'I~)' to be excited by .mctastable Xe(Za). Comparison of the quenching of sensitized and unsensitized CO fluorescence by He, Ar and N, indicated that LI quenchable precursor is necessary Lr the sensitized phcnoinerton, nnd the precursor was iden tifled as a tong-:-lived (T> 2 X IW6 SC':) cuiiision complex ut XC(I,) and CO, We here report observations madr on the sc~lsitizcd emission using n modulated xenon rescinancc Iamp 121 nnd a phase shift rrietlwd to pvc kinetic IZIformation about proccssc:a invdvu~g the ,YcKU* wIIIsion complex. i6.
Temperature dependence measurements between 78 and 180 K were carried out on the decay of the 420... more Temperature dependence measurements between 78 and 180 K were carried out on the decay of the 420 nm luminescence emitted by purified polycrystalline H 2 O ice, irradiated at 260 nm. Previous work at 78 K showed that a biexponential decay model fitted that luminescence decay quite well. This was also found to be the case at all of the temperatures studied in the present work, the mean lifetimes of the two decays being 0.8 (0.1 s and 2.5 (0.4 s. Activation energies were found to be negligible in both cases, being less than the experimental error of 0.003 eV. Such low values are consistent with the rate-limiting step being a lightemitting electronic transition rather than a chemical or diffusional step. The 420 nm luminescence is attributed to the spin forbidden 4 Σf X 2 Π transition of OH radicals from their excited state back to the ground state.
Data for the quenching of fluorescence excited by 58.4 nm irradiation of CO2, N2O, and N2 have be... more Data for the quenching of fluorescence excited by 58.4 nm irradiation of CO2, N2O, and N2 have been recalculated in the light of improved absorption coefficients for 58.4 nm radiation. The new rate constants for quenching of CO2+ are in better agreement with results obtained from experiments with electron beam excitation; for N2+ the disagreement is greater than before.
... Volume 45, number 2 CHEMICAL PHYSICS LETTERS 15 January 1977 THE EXCITED MERCURY-AMMONIA EMIS... more ... Volume 45, number 2 CHEMICAL PHYSICS LETTERS 15 January 1977 THE EXCITED MERCURY-AMMONIA EMISSION AT LOW PRESSURE Anthony B. CALLEAR and Colin G. FREEMAN* Physical Chemistry Department ... McEwan, RFC Claridge and LF Phillips, Chem. Fhys. ...
ChemInform Abstract Untersuchung des spektralen und des Abklingverhultens der wichtigsten Eimssio... more ChemInform Abstract Untersuchung des spektralen und des Abklingverhultens der wichtigsten Eimssionen zum Zwecke der Identifizierung der emittierenden Spezies und der Bestimmung der Löschgeschwindigkeit durch Wasserdampf.
In a previous study,' the reaction of oxygen atoms with I2 was found to yield mainly solid 120s o... more In a previous study,' the reaction of oxygen atoms with I2 was found to yield mainly solid 120s on the wall of the reaction vessel. The present work was undertaken to find whether, in the reaction with ICN, iodine oxide could be made to deposit on the wall and leave CN radicals behind in the gas phase. If this happened, the reaction might provide a convenient source of CN radicals in a flow system. Oxygen atoms were produced either by discharging 0 2 or, in the absence of 0 2 , by titrating nitrogen atoms with Matheson prepurified nitrogen and ultrahigh-purity oxygen were used. Nitric oxide was purified by distillation from soda-asbestos. ICN was prepared by the method of Goy, Shaw, and Pritchard.3 (1) D. I. Walton and L. F.
The oxidants produced by radiolysis and photolysis in the icy surface of Europa may be necessary ... more The oxidants produced by radiolysis and photolysis in the icy surface of Europa may be necessary to sustain carbon-based biochemistry in Europa's putative subsurface ocean. Because the subduction of oxidants to the ocean presents considerable thermodynamic challenges, we examine the formation of oxygen and related species in Europa's surface ice with the goal of characterizing the chemical state of the irradiated material. Relevant spectral observations of Europa and the laboratory data on the production of oxygen and related species are first summarized. Since the laboratory data are incomplete, we examine the rate equations for formation of oxygen and its chemical precursors by radiolysis and photolysis. Measurements and simple rate equations are suggested that can be used to characterize the production of oxidants in Europa's surface material and the chemical environment produced by radiolysis. Possible precursor molecules and the role of radical trapping are examined. The possibility of oxygen reactions on grain surfaces in Europa's regolith is discussed, and the earlier estimates of the supply of O 2 to the atmosphere are increased.
The luminescence arising from the excitation by 0.53 MeV electrons of vacuum deposited polycrysta... more The luminescence arising from the excitation by 0.53 MeV electrons of vacuum deposited polycrystalline ice at 77 K, has been studied as a function of deposition rate and ice thickness. Changes in deposition rate from 0.03 to 17 mm h−1, at various constant sample thicknesses, affected the luminescence intensity, I, but did not significantly affect the decay half-life, nor C
D2O vapor was irradiated using a 0.53 MeV pulsed electron beam and the 200–900 nm wavelength rang... more D2O vapor was irradiated using a 0.53 MeV pulsed electron beam and the 200–900 nm wavelength range was examined for luminescence emission from excited fragments. Spectral lines of the OD (C 2∑+→A 2∑+) and the OD (A 2∑+→X 2Π) transitions were observed, as were the Balmer transitions of deuterium between n=6→n=2 and n=3→n=2, and the oxygen transitions O+(3p 4D0→3s 4P),O(3p 5P→3s 5S0), and O(3p 3P→3s 3S0). Values were obtained for the natural lifetimes, quenching rate constants, and quenching cross sections at 298 K for the majority of the above excited species. The natural lifetimes and quenching data obtained for the transitions of excited OD and oxygen species were, as expected, similar to the values obtained for the corresponding species in H2O vapor. However, Balmer D transitions exhibited shorter natural lifetimes and smaller quenching cross sections than the corresponding Balmer H transitions. The differences in quenching rate were much larger than the effect of isotopic substitution on collision frequency. Both lifetime and quenching differences were attributed to greater population of the p sublevels in excited D as compared with H.
Luminescence peaking at 405 nm was observed when thin films of amorphous or polycrystalline ice a... more Luminescence peaking at 405 nm was observed when thin films of amorphous or polycrystalline ice at 97 K were irradiated with a pulsed beam of 0.53 MeV electrons. These emissions differed from the luminescence emitted by crystalline ice in that memory effects were not observed; the peak wavelengths were red shifted by ∼20 nm; and the half-lives were 6–9 ns instead of ∼400 ns. The emission spectra of polycrystalline ice samples produced by rapid deposition or by annealing amorphous ice were similar, but both had substantially lower intensities than amorphous ice spectra.
Journal of the American Society for Mass Spectrometry, May 1, 2001
The FA-SIFT experiment at Canterbury was used to determine some of the principal termolecular ion... more The FA-SIFT experiment at Canterbury was used to determine some of the principal termolecular ion-molecule reactions that occur in the atmosphere of Titan, Saturn's satellite. The experiments were performed using both a pure nitrogen bath gas and a pure helium bath gas. The reactions of the ions N
Rate coefficients are reported for a number of proton-transfer reactions with formic acid. These ... more Rate coefficients are reported for a number of proton-transfer reactions with formic acid. These reactions can be represented by the general equation XHt +HCOOH-, (HCOOH)H+ +X (X = CH4, H20, Nz, CO, HCN, HCHO, CH,OH and H2S). Reasonable agreement was obtained between our observed results and predictions based on the average-dipole-orientation (ADO) model except that ADO theory may slightly underestimate the collision rate.
Aus derÄnderung der Lumineszenzausbeute mit der Alkoholstruktur wird gefolgert, dass der mit der ... more Aus derÄnderung der Lumineszenzausbeute mit der Alkoholstruktur wird gefolgert, dass der mit der Lumineszenz konkurrierende Hauptprozess gewöhnlich die Abspaltung eines oe-H-Atoms durch ein metastabiles Hg(3P0)-Atom ist, das bei der Löschung von Hg(3P,) entsteht.
Water vapor was excited by a 0.53 MeV pulsed electron beam and examined for luminescence emission... more Water vapor was excited by a 0.53 MeV pulsed electron beam and examined for luminescence emission in the 360–600 nm region. Spectral lines arising from the Balmer transitions H(n=4→n=2), H(n=5→n=2), and H(n=6→n=2) of the hydrogen atom and the transitions 3p4D05/2→3s4P3/2, 3p4D07/2→ 3s4P5/2, and 3p4D01/2→3s4P1/2 of the O+ ion were observed. The Balmer lines were found to be quenched by water vapor with rate constants at 293 K of (9.77±0.26)×10−9, (10.67±0.45)×10−9, and (12.3±2.3)×10−9 cm3 molecule−1 s−1, respectively. The excited O+ ions were also quenched strongly by water vapor but line intensities were insufficient for rate measurements to be carried out.
Journal of Photochemistry and Photobiology, Apr 1, 1984
... 5 TI Quickenden, JA Irvin and DF Sangster, J. Client Plays., 69 (1978) 4395. 6 G. Herzberg, M... more ... 5 TI Quickenden, JA Irvin and DF Sangster, J. Client Plays., 69 (1978) 4395. 6 G. Herzberg, Molecular Spectra and Molecular Structure, Vol. I, The Spectra of Diatomic Molecules, VanNostrand Reinhold, New York, 1966. References. 1. G. Herzberg J. Chem. Phys. ...
S!E;E~T [ 11 hns reported emissions from three upper triplet levels cs: CO, d 3A, e 32: and ZI' 3... more S!E;E~T [ 11 hns reported emissions from three upper triplet levels cs: CO, d 3A, e 32: and ZI' 32, when CCS undergocs collision with xenon atoms excited to the IL, level by the xenon resonance tine at I47 nm. The observed bands arise from transitions to t!le lowest tripfel ievel, a 311. The excited slates are !W high if1 LVIL'I~)' to be excited by .mctastable Xe(Za). Comparison of the quenching of sensitized and unsensitized CO fluorescence by He, Ar and N, indicated that LI quenchable precursor is necessary Lr the sensitized phcnoinerton, nnd the precursor was iden tifled as a tong-:-lived (T> 2 X IW6 SC':) cuiiision complex ut XC(I,) and CO, We here report observations madr on the sc~lsitizcd emission using n modulated xenon rescinancc Iamp 121 nnd a phase shift rrietlwd to pvc kinetic IZIformation about proccssc:a invdvu~g the ,YcKU* wIIIsion complex. i6.
Temperature dependence measurements between 78 and 180 K were carried out on the decay of the 420... more Temperature dependence measurements between 78 and 180 K were carried out on the decay of the 420 nm luminescence emitted by purified polycrystalline H 2 O ice, irradiated at 260 nm. Previous work at 78 K showed that a biexponential decay model fitted that luminescence decay quite well. This was also found to be the case at all of the temperatures studied in the present work, the mean lifetimes of the two decays being 0.8 (0.1 s and 2.5 (0.4 s. Activation energies were found to be negligible in both cases, being less than the experimental error of 0.003 eV. Such low values are consistent with the rate-limiting step being a lightemitting electronic transition rather than a chemical or diffusional step. The 420 nm luminescence is attributed to the spin forbidden 4 Σf X 2 Π transition of OH radicals from their excited state back to the ground state.
Data for the quenching of fluorescence excited by 58.4 nm irradiation of CO2, N2O, and N2 have be... more Data for the quenching of fluorescence excited by 58.4 nm irradiation of CO2, N2O, and N2 have been recalculated in the light of improved absorption coefficients for 58.4 nm radiation. The new rate constants for quenching of CO2+ are in better agreement with results obtained from experiments with electron beam excitation; for N2+ the disagreement is greater than before.
... Volume 45, number 2 CHEMICAL PHYSICS LETTERS 15 January 1977 THE EXCITED MERCURY-AMMONIA EMIS... more ... Volume 45, number 2 CHEMICAL PHYSICS LETTERS 15 January 1977 THE EXCITED MERCURY-AMMONIA EMISSION AT LOW PRESSURE Anthony B. CALLEAR and Colin G. FREEMAN* Physical Chemistry Department ... McEwan, RFC Claridge and LF Phillips, Chem. Fhys. ...
ChemInform Abstract Untersuchung des spektralen und des Abklingverhultens der wichtigsten Eimssio... more ChemInform Abstract Untersuchung des spektralen und des Abklingverhultens der wichtigsten Eimssionen zum Zwecke der Identifizierung der emittierenden Spezies und der Bestimmung der Löschgeschwindigkeit durch Wasserdampf.
In a previous study,' the reaction of oxygen atoms with I2 was found to yield mainly solid 120s o... more In a previous study,' the reaction of oxygen atoms with I2 was found to yield mainly solid 120s on the wall of the reaction vessel. The present work was undertaken to find whether, in the reaction with ICN, iodine oxide could be made to deposit on the wall and leave CN radicals behind in the gas phase. If this happened, the reaction might provide a convenient source of CN radicals in a flow system. Oxygen atoms were produced either by discharging 0 2 or, in the absence of 0 2 , by titrating nitrogen atoms with Matheson prepurified nitrogen and ultrahigh-purity oxygen were used. Nitric oxide was purified by distillation from soda-asbestos. ICN was prepared by the method of Goy, Shaw, and Pritchard.3 (1) D. I. Walton and L. F.
The oxidants produced by radiolysis and photolysis in the icy surface of Europa may be necessary ... more The oxidants produced by radiolysis and photolysis in the icy surface of Europa may be necessary to sustain carbon-based biochemistry in Europa's putative subsurface ocean. Because the subduction of oxidants to the ocean presents considerable thermodynamic challenges, we examine the formation of oxygen and related species in Europa's surface ice with the goal of characterizing the chemical state of the irradiated material. Relevant spectral observations of Europa and the laboratory data on the production of oxygen and related species are first summarized. Since the laboratory data are incomplete, we examine the rate equations for formation of oxygen and its chemical precursors by radiolysis and photolysis. Measurements and simple rate equations are suggested that can be used to characterize the production of oxidants in Europa's surface material and the chemical environment produced by radiolysis. Possible precursor molecules and the role of radical trapping are examined. The possibility of oxygen reactions on grain surfaces in Europa's regolith is discussed, and the earlier estimates of the supply of O 2 to the atmosphere are increased.
The luminescence arising from the excitation by 0.53 MeV electrons of vacuum deposited polycrysta... more The luminescence arising from the excitation by 0.53 MeV electrons of vacuum deposited polycrystalline ice at 77 K, has been studied as a function of deposition rate and ice thickness. Changes in deposition rate from 0.03 to 17 mm h−1, at various constant sample thicknesses, affected the luminescence intensity, I, but did not significantly affect the decay half-life, nor C
D2O vapor was irradiated using a 0.53 MeV pulsed electron beam and the 200–900 nm wavelength rang... more D2O vapor was irradiated using a 0.53 MeV pulsed electron beam and the 200–900 nm wavelength range was examined for luminescence emission from excited fragments. Spectral lines of the OD (C 2∑+→A 2∑+) and the OD (A 2∑+→X 2Π) transitions were observed, as were the Balmer transitions of deuterium between n=6→n=2 and n=3→n=2, and the oxygen transitions O+(3p 4D0→3s 4P),O(3p 5P→3s 5S0), and O(3p 3P→3s 3S0). Values were obtained for the natural lifetimes, quenching rate constants, and quenching cross sections at 298 K for the majority of the above excited species. The natural lifetimes and quenching data obtained for the transitions of excited OD and oxygen species were, as expected, similar to the values obtained for the corresponding species in H2O vapor. However, Balmer D transitions exhibited shorter natural lifetimes and smaller quenching cross sections than the corresponding Balmer H transitions. The differences in quenching rate were much larger than the effect of isotopic substitution on collision frequency. Both lifetime and quenching differences were attributed to greater population of the p sublevels in excited D as compared with H.
Luminescence peaking at 405 nm was observed when thin films of amorphous or polycrystalline ice a... more Luminescence peaking at 405 nm was observed when thin films of amorphous or polycrystalline ice at 97 K were irradiated with a pulsed beam of 0.53 MeV electrons. These emissions differed from the luminescence emitted by crystalline ice in that memory effects were not observed; the peak wavelengths were red shifted by ∼20 nm; and the half-lives were 6–9 ns instead of ∼400 ns. The emission spectra of polycrystalline ice samples produced by rapid deposition or by annealing amorphous ice were similar, but both had substantially lower intensities than amorphous ice spectra.
Journal of the American Society for Mass Spectrometry, May 1, 2001
The FA-SIFT experiment at Canterbury was used to determine some of the principal termolecular ion... more The FA-SIFT experiment at Canterbury was used to determine some of the principal termolecular ion-molecule reactions that occur in the atmosphere of Titan, Saturn's satellite. The experiments were performed using both a pure nitrogen bath gas and a pure helium bath gas. The reactions of the ions N
Rate coefficients are reported for a number of proton-transfer reactions with formic acid. These ... more Rate coefficients are reported for a number of proton-transfer reactions with formic acid. These reactions can be represented by the general equation XHt +HCOOH-, (HCOOH)H+ +X (X = CH4, H20, Nz, CO, HCN, HCHO, CH,OH and H2S). Reasonable agreement was obtained between our observed results and predictions based on the average-dipole-orientation (ADO) model except that ADO theory may slightly underestimate the collision rate.
Aus derÄnderung der Lumineszenzausbeute mit der Alkoholstruktur wird gefolgert, dass der mit der ... more Aus derÄnderung der Lumineszenzausbeute mit der Alkoholstruktur wird gefolgert, dass der mit der Lumineszenz konkurrierende Hauptprozess gewöhnlich die Abspaltung eines oe-H-Atoms durch ein metastabiles Hg(3P0)-Atom ist, das bei der Löschung von Hg(3P,) entsteht.
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