A study of radiative and collisional decay of Pb atoms by time-resolved laser spectroscopy

1984 ◽  
Vol 62 (12) ◽  
pp. 1616-1621 ◽  
Author(s):  
D. H. Giers ◽  
J. B. Atkinson ◽  
L. Krause
Keyword(s):  
Cross Sections ◽  
Decay Constant ◽  
Radiative Lifetime ◽  
Resonance Wavelength ◽  
Nitrogen Laser ◽  
Buffer Gas ◽  
Time Resolved ◽  
Upper Limit ◽  
Least Squares Fit ◽  
Gas Pressures

The 6p7s[Formula: see text] state of atomic Pb was populated by irradiation of Pb vapor by the frequency-doubled output of a pulsed nitrogen laser–pumped dye laser at the resonance wavelength λ = 2833 Å, and the resulting fluorescent decay was monitored using the method of delayed coincidences. A least squares fit to the observed time-decay spectrum yielded the decay constant and gave the radiative lifetime of the [Formula: see text] state, τ = 5.85 ± 0.20 ns. The dependence of the decay constant on buffer gas pressures was also investigated, yielding the total depopulation (quenching) cross sections Q = 0.31 ± 0.10 Å2 and 12.2 ± 1.0 Å2 for collisions with H2 and N2, respectively. An upper limit (Q < 0.2 Å2) for the He quenching cross section was also determined.

Cross sections for quenching of Pb 6p7s3P1 atoms by collisions with CH4, CO, and CO2 molecules

1985 ◽  
Vol 63 (8) ◽  
pp. 1110-1111
Author(s):  
D. H. Giers ◽  
J. B. Atkinson ◽  
L. Krause
Keyword(s):  
Fluorescence Spectroscopy ◽  
Cross Sections ◽  
Laser Light ◽  
Buffer Gas ◽  
Time Resolved Fluorescence ◽  
Time Resolved ◽  
Decay Constants ◽  
Gas Pressures

Pb vapor mixed with a buffer gas was irradiated with pulses of laser light so as to populate the [Formula: see text] state, whose radiative and collisional decay was monitored by the method of time-resolved fluorescence spectroscopy. The variation of the measured decay constants with buffer-gas pressures yielded the total depopulation (quenching) cross sections Q = 3.32 ± 0.25, 25.6 ± 2.2, and 84.1 ± 8.4 Å2 for collisions with CH4, CO, and CO2, respectively.

Disorientation of Cs(62P1/2) atoms, induced in collisions with noble gases

1976 ◽  
Vol 54 (7) ◽  
pp. 748-752 ◽  
Author(s):  
B. Niewitecka ◽  
L. Krause
Keyword(s):  
Cross Sections ◽  
Noble Gas ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Buffer Gas ◽  
Resonance Fluorescence ◽  
Circularly Polarized ◽  
Low Field ◽  
Good Agreement ◽  
Gas Pressures

The disorientation of 62P1/2 cesium atoms, induced in collisions with noble gas atoms in their ground states, was systematically investigated by monitoring the depolarization of cesium resonance fluorescence in relation to noble gas pressures. The Cs atoms, contained together with a buffer gas in a fluorescence cell and located in zero magnetic field, were excited and oriented by irradiation with circularly polarized 8943 Å resonance radiation, and the resonance fluorescence, emitted in an approximately backward direction, was analyzed with respect to circular polarization. The experiments yielded the following disorientation cross sections which have been corrected for the effects of nuclear spin: Cs–He: 4.9 ± 0.7 Å2; Cs–Ne: 2.1 ± 0.3 Å2; Cs–Ar: 5.6 ± 0.8 Å2; Cs–Kr: 5.8 ± 0.9 Å2; Cs–Xe: 6.3 ± 0.9 Å2. The results are in good agreement with most of the available zero-field and low-field data.

scholarly journals Time-Resolved Measurements and Master Equation Modelling of the Unimolecular Decomposition of CH3OCH2

2020 ◽  
Vol 234 (7-9) ◽  
pp. 1233-1250 ◽  
Author(s):  
Arrke J. Eskola ◽  
Mark A. Blitz ◽  
Michael J. Pilling ◽  
Paul W. Seakins ◽  
Robin J. Shannon
Keyword(s):  
Energy Transfer ◽  
Master Equation ◽  
Rate Coefficient ◽  
Zero Point ◽  
Buffer Gas ◽  
Unimolecular Decomposition ◽  
Time Resolved ◽  
Point Energy ◽  
Wide Range ◽  
Transfer Parameters

AbstractThe rate coefficient for the unimolecular decomposition of CH3OCH2, k1, has been measured in time-resolved experiments by monitoring the HCHO product. CH3OCH2 was rapidly and cleanly generated by 248 nm excimer photolysis of oxalyl chloride, (ClCO)2, in an excess of CH3OCH3, and an excimer pumped dye laser tuned to 353.16 nm was used to probe HCHO via laser induced fluorescence. k1(T,p) was measured over the ranges: 573–673 K and 0.1–4.3 × 1018 molecule cm−3 with a helium bath gas. In addition, some experiments were carried out with nitrogen as the bath gas. Ab initio calculations on CH3OCH2 decomposition were carried out and a transition-state for decomposition to CH3 and H2CO was identified. This information was used in a master equation rate calculation, using the MESMER code, where the zero-point-energy corrected barrier to reaction, ΔE0,1, and the energy transfer parameters, ⟨ΔEdown⟩ × Tn, were the adjusted parameters to best fit the experimental data, with helium as the buffer gas. The data were combined with earlier measurements by Loucks and Laidler (Can J. Chem.1967, 45, 2767), with dimethyl ether as the third body, reinterpreted using current literature for the rate coefficient for recombination of CH3OCH2. This analysis returned ΔE0,1 = (112.3 ± 0.6) kJ mol−1, and leads to $k_{1}^{\infty}(T)=2.9\times{10^{12}}$ (T/300)2.5 exp(−106.8 kJ mol−1/RT). Using this model, limited experiments with nitrogen as the bath gas allowed N2 energy transfer parameters to be identified and then further MESMER simulations were carried out, where N2 was the buffer gas, to generate k1(T,p) over a wide range of conditions: 300–1000 K and N2 = 1012–1025 molecule cm−3. The resulting k1(T,p) has been parameterized using a Troe-expression, so that they can be readily be incorporated into combustion models. In addition, k1(T,p) has been parametrized using PLOG for the buffer gases, He, CH3OCH3 and N2.

scholarly journals Time-Resolved Investigation of the Molecular Chemiluminescence SrI(A2∏1/2,3,2,B2∑+→X2∑+) and the Atomic Resonance Fluorescence Sr(53P1→51S0) Following The Pulsed Dye Laser Generation Of Sr(53PJ) in the Presence of CF3I

1995 ◽  
Vol 16 (2) ◽  
pp. 121-138 ◽  
Author(s):  
S. Antrobus ◽  
D. Husain ◽  
Jie Lei ◽  
F. Castaño ◽  
M. N. Sanchez Rayo
Keyword(s):  
Ground State ◽  
Branching Ratio ◽  
Atomic Emission ◽  
Electronic Energy ◽  
Dye Laser ◽  
Pulsed Dye Laser ◽  
Laser Generation ◽  
Buffer Gas ◽  
Resonance Fluorescence ◽  
Time Resolved

A time-resolved investigation is presented of the electronic energy distribution in SrI following the collision of the optically metastable strontium atom, Sr [5s5p(3PJ)], with the molecule CF3I. Sr[5s5p(3PJ)], 1.807 eV above its 5s2(1S0) electronic ground state, was generated by pulsed dye-laser excitation of ground state strontium vapour to the Sr(53P1) state at , λ =689.3 nm {Sr(53P1←51S0)} at elevated temperature (840 K) in the presence of excess helium buffer gas in which rapid Boltzmann equilibration within the 53PJ spin-orbit manifold takes place. Time resolved atomic emission from Sr(53P1→51S0) at the resonance transition and the molecular chemiluminescence from SrI(A2∏1,2,3/2,B2∑+→X2∑+) resulting from reaction of the excited atom with CF3I were recorded and shown to be exponential in character. SrI in the A2∏1/2,3/2 (172.5, 175.4 kJ mol-1) and B2∑+ (177.3 kJ mol-1) states are energetically accessible on collision by direct-I-atomic abstraction between Sr(3P) and CF3I. The first-order decay coefficients for the atomic and molecular emissions are found to be equal under identical conditions and hence SrI(A2∏1/2,3/2, B2∑+) are shown to arise from direct I- atom abstraction reactions. The molecular systems recorded were SrI (A2∏1/2→X2∑+, Δv=0, λ=694 nm), SrI(A2∏3/2→X2∑+, Δv=0, λ=677 nm) and SrI(B2∑+→X2∑+) (Δv=0, λ=674 nm), dominated by the Δv=0 sequences on account of Franck-Condon considerations. The combination of integrated m61ecular and atomic intensity measurements yields estimates of the branching ratios into the specific electronic states, A1/2, A3/2 and B, arising from Sr(53PJ)+CF3I which are found to be as follows: A1/2,1.2 × 10-2; A3/2, 6.7 × 10-3; B, 5.1 × 10-3 yielding ∑SrI(A1/2+A3/2+B)=2.4 × 10-2. As only the X, A and B states SrI are accessible on reaction, assuming that the removal of Sr(53PJ) occurs totally by chemical removal, this yields an upper limit for the branching ratio into the ground state of ca. 98%. The present results are compared with previous time-resolved measurements on excited states of strontium halides that we have reported on various halogenated species resulting from reactions of Sr(53PJ), together with analogous chemiluminescence studies on Sr(3PJ) and Ca(43PJ) from molecular beam measurements.

scholarly journals Fiber-Optic Time-Resolved Fluorescence Sensor for in Vitro Serotonin Determination

1993 ◽  
Vol 47 (5) ◽  
pp. 590-597 ◽  
Author(s):  
Stephane Mottin ◽  
Canh Tran-Minh ◽  
Pierre Laporte ◽  
Raymond Cespuglio ◽  
Michel Jouvet
Keyword(s):  
Chemical Sensor ◽  
Fiber Optic ◽  
Fiber Optic Sensor ◽  
Excitation Wavelength ◽  
Nitrogen Laser ◽  
Time Resolved ◽  
Temporal Effects ◽  
Starting Point

At pH 7 and with the excitation at wavelengths above 315 nm, previously unreported fluorescence of 5-HT (5-hydroxytryptamine) is observed. Two fluorescence bands were observed for 5-HT; the first emits at around 390 nm with an associated lifetime near 1 ns, and the other (well known) emits at 340 nm with an associated lifetime of 2.7 ns. With both static and time-resolved fluorescences, the spectral and temporal effects of the excitation wavelength were studied between 285 and 340 nm. With these basic spectroscopic properties as a starting point, a fiber-optic chemical sensor (FOCS) was developed in order to measure 5-HT with a single-fiber configuration, nitrogen laser excitation, and fast digitizing techniques. Temporal effects including fluorescence of the optical fiber were studied and compared with measurements both directly in cuvette and through the fiber-optic sensor. Less than thirty seconds are required for each measurement. A detection limit of 5-HT is reached in the range of 5 μM. Our system, with an improved sensitivity, could therefore be a possible and convenient “tool” for in vivo determination of 5-HT.

scholarly journals Turbulent drag reduction by polymer additives in parallel-shear flows

2017 ◽  
Vol 827 ◽  
Author(s):  
Bayode E. Owolabi ◽  
David J. C. Dennis ◽  
Robert J. Poole
Keyword(s):  
Drag Reduction ◽  
Cross Sections ◽  
Shear Flows ◽  
Extensional Flow ◽  
Relaxation Times ◽  
Weissenberg Number ◽  
Mechanical Degradation ◽  
Turbulent Drag Reduction ◽  
Time Resolved ◽  
Turbulent Drag

In this study, we experimentally investigate the turbulent drag-reduction (DR) mechanism in flow through ducts of circular, rectangular and square cross-sections using two grades of polyacrylamide in aqueous solution having different molecular weights and various semidilute concentrations. Specifically, we explore the relationship between drag reduction and fluid elasticity, purposely exploiting the mechanical degradation of polymer molecules to vary their rheological properties. We also obtain time-resolved velocity data for various DR levels using particle image velocimetry and laser Doppler velocimetry. Elasticity is quantified via relaxation times determined from uniaxial extensional flow using a capillary breakup apparatus. A plot of DR against Weissenberg number ($Wi$) is found to approximately collapse the data, with the onset of DR occurring at $Wi\approx 0.5$ and the maximum drag-reduction asymptote being approached for $Wi\gtrsim 5$. Thus quantitative predictions of DR in a range of shear flows can be made from a single measurable material property of a polymer solution, at least for this particular flexible linear polymer.

Absorption cross sections and V-T relaxation rates in SF6—Ar mixtures by time-resolved infrared multiphoton absorption

1986 ◽  
Vol 108 (1) ◽  
pp. 167-177 ◽  
Author(s):  
M. Lenzi ◽  
E. Molinari ◽  
G. Piciacchia ◽  
V. Sessa ◽  
M.L. Terranova
Keyword(s):  
Cross Sections ◽  
Multiphoton Absorption ◽  
Absorption Cross ◽  
Relaxation Rates ◽  
Time Resolved

scholarly journals Pulse Radiolysis Studies of Collisional Deexcitation of Ne(3P1) by H2

2015 ◽  
Vol 19 (1) ◽  
pp. 75-78
Author(s):  
Deba Bahadur Khadka
Keyword(s):  
Optical Absorption ◽  
Absorption Spectroscopy ◽  
Cross Sections ◽  
Pulse Radiolysis ◽  
Science And Technology ◽  
Optical Absorption Spectroscopy ◽  
Time Resolved ◽  
Collisional Energy ◽  
The Mean ◽  
Collisional Deexcitation

The cross sections for the deexcitation of Ne(3P1) by H2 have been measured as a function of the mean collisional energy in the range of 17.3-37.9 meV or in the temperature range from 134 K to 293 K using a pulse radiolysis method as combined with time-resolved optical absorption spectroscopy. The deexcitation cross sections are in the range of 2.1- 5.6 Å2 for Ne(3P1) and nearly constant or increase slightly with increasing the collisional energy.Journal of Institute of Science and Technology, 2014, 19(1): 75-78

scholarly journals Determination of the absorption cross-sections of higher order iodine oxides at 355 nm and 532 nm

2020 ◽  
Author(s):  
Thomas R. Lewis ◽  
Juan Carlos Gómez Martin ◽  
Mark A. Blitz ◽  
Carlos A. Cuevas ◽  
John M. C. Plane ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Atmospheric Chemistry ◽  
Absorption Cross Section ◽  
Absorption Cross ◽  
Time Resolved ◽  
Flight Mass Spectrometry ◽  
Iodine Oxides ◽  
Photo Ionization

Abstract. Iodine oxides (IxOy) play an important role in the atmospheric chemistry of iodine. They are initiators of new particle formation events in the coastal and polar boundary layer and act as iodine reservoirs in tropospheric ozone-depleting chemical cycles. Despite the importance of the aforementioned processes, the photochemistry of these molecules has not been studied in detail previously. Here, we report the first determination of the absorption cross sections of IxOy, x = 2, 3, 5, y = 1–12 at λ = 355 nm by combining pulsed laser photolysis of I2/O3 gas mixtures in air with time-resolved photo-ionization time-of-flight mass spectrometry, using NO2 actinometry for signal calibration. The oxides selected for absorption cross section determinations are those presenting the strongest signals in the mass spectra, where signals containing 4 iodine atoms are absent. The method is validated by measuring the absorption cross section of IO at 355 nm, σ355 nm, IO = (1.2 ± 0.1) ×  10–18 cm2, which is found to be in good agreement with the most recent literature. The results obtained are: σ355 nm, I2O3 

Sign in / Sign up

Export Citation Format

Share Document