Collisional Deactivation Research Articles

Luminescence studies of lanthanide ion binding to parvalbumin.

Luminescence methods were used to examine the interaction of Eu(III) and Tb(III) with parvalbumin isozyme III from pike (Esox lucius). The bound lanthanide ions were excited both directly, via laser irradiation, and indirectly, via fluorescence energy transfer from adjacent phenylalanine residues. At high (175 microM) protein concentrations, the lanthanide titration curves exhibited pronounced quenching of luminescence at Ln3+:parvalbumin ratios above 2:1, in agreement with earlier reports (Donato, H., Jr., and Martin, R. B. (1974) Biochemistry 13, 4575-4579). However, in experiments performed with lower concentrations (10 microM), the titrations were well behaved and indicated a lanthanide:protein stoichiometry of 2:1. Equilibrium dialysis measurements performed with Eu(III) ruled out the existence of a third strong binding site which could cause the quenching of the luminescence at high protein concentrations. Similarly, careful analysis of the spectrum that results from direct excitation of the 7F0----5D0 transition of parvalbumin-bound Eu3+ ion revealed no peak attributable to a third Ln3+-binding site. The peak which has been construed by others (Rhee, M.-J., Sudnick, D. R., Arkle, V. K., and Horrocks, W. DeW., Jr. (1981) Biochemistry 20, 3328-3334) as evidence for a third site was shown to result from a pH-dependent spectral transition involving the europium ions bound at the CD and EF sites. Luminescent lifetime measurements performed on Tb(III)/parvalbumin solutions follow Stern-Volmer quenching kinetics at terbium:protein ratios in excess of 2:1, suggesting that the quenching results from collisional deactivation of the tightly bound ions by excess terbium ion free in solution.

ArF laser flash photolysis of hexafluorobenzene vapor: Formation of hot molecules and their collisional relaxation

Time-resolved absorption spectra of hexafluorobenzene vapor have been observed in the time range of 0–2 μs after pulsed ArF laser (193 nm) excitation. The absorption spectrum observed at the time t=0 is attributed to HFB* (S0) (hot hexafluorobenzene with an internal energy of 639 kJ/mol). This transient absorption spectrum can be simulated as a part of the spectrum of the S3(1E1u)←S0 transition at 3050 K on the basis of a modified Sulzer–Wieland model. The collisional deactivation of HFB* molecules is explained in terms of an energy transfer model which assumes that the energy removed per collision depends upon the internal energy.

Vibrational energy distribution of methylene-d2(1A1) from ketene-d2 photolysis upon reaction with cyclobutane. A chemically activated methylcyclobutane study

The results of a study of chemically activated methylcyclobutane and methylcyclobutane-d/sub 2/ from the 337-, 334-, and 313-nm photolyses of ketene or ketene-d/sub 2/ in the presence of cyclobutane, tetramethylsilane, and oxygen are presented. The collisional deactivation of the chemically activated molecules was found to occur in steps of 6 +/- 2 kcal/mol. A critical examination of the uncertainties in collisional deactivation stepsize determinations in chemical activation systems is given. The vibrational energy distribution of the CH/sub 2/(/sup 1/A/sub 1/) and CD/sub 2/(/sup 1/A/sub 1/) at the time of reaction with cyclobutane are determined and discussed. The distributions were found to broaden giving increasing average methylene energies with increasing photon energies and with deuterium substitution on the CH/sub 2/. An interesting quantum statistical isotope effect on the width of these distributions in going from the 337- to 313-nm photolysis systems is observed and explained in terms of the CH/sub 2/(/sup 1/A/sub 1/) and CD/sub 2/(/sup 1/A/sub 1/) vibrational frequency models. This is an energy partitioning isotope effect on CH/sub 2/CO vs. CD/sub 2/CO photodissociations. A statistical energy partitioning model for CH/sub 2/CO and CD/sub 2/CO photodissociation was found to give generally narrower methylene vibrational energy distributions and lower average energiesmore » than observed. 19 references, 10 figures, 6 tables.« less

Time Resolved Two‐Color Multiphoton Ionization Studies on the Intramolecular Dynamics of Cycloheptatrienes

AbstractOne and two color multiphotonionization experiments in cycloheptatriene, methyl‐, ethyl‐, and isopropyl‐cycloheptatriene are reported. Rate constants for the fast internal conversions S1 → S0 of these molecules were determined. A collisional deactivation process in the pathway of time delayed two color multiphoton ionization is observed.

Quenching of the 1Σ+g state in liquid oxygen isotopes

A nonexponential decay of the 1Σ+g state in liquid oxygen is observed for high number densities (≫1017 cm−3) of excited O2 molecules. At low excitation intensities the decay of O2(1Σ+g) is exponential with rate constants 1.2×105 and 6.7×103 s−1 for liquid natural O2 and 18O2, respectively (at T=77 K). There is direct experimental evidence that O2(1Σ+g) is quenched to the 1Δg state. Calculations of the ratio of the transition probabilities for collisional deactivation of 16O2(1Σ+g) and 18O2(1Σ+g) are in satisfactory agreement with the experimental results.

Measurement of the absolute third-order rate constant for the reaction between Cs + OH + He determined by time-resolved molecular resonance-fluorescence spectroscopy, OH(A2Σ+–X2Π), coupled with steady atomic resonance fluorescence, Cs(72PJ–62S1/2)

We present the first direct measurement of the absolute third-order rate constant (k1) for the reaction Cs + OH + He → CsOH + He (T= 481 K) completing the series of analogous studies with the present experimental system we have also described for Na, K and Rb. OH(X2Π), generated by the pulsed irradiation of H2O vapour through CaF2 optics in a slow-flow system, kinetically equivalent to a static system, was monitored by time-resolved resonance fluorescence at λ= 307 nm [OH(A2Σ+–X2Π), (0, 0)] in the presence of an excess of atomic caesium derived from a heat-pipe oven and helium buffer gas. The atomic caesium was monitored in the steady mode using atomic resonance fluorescence of the unresolved Rydberg doublet at λ= 457 nm [Cs(72PJ– 62S1/2)] coupled with phase-sensitive detection. The following value of k1 was obtained: k1(481 K)=(10.0 ± 1.5)× 10–31 cm6 molecule–2 s–1. This result was extrapolated to 2000 K using the unimolecular reaction rate theory by Troe, including the quantitative effects of hindered rotation on the low-frequency bending modes of CsOH. We have employed the same formalism to calculate the rate constant for the reaction between Li + OH + He at 500 and 2000 K. The resulting calculated temperature dependences of the third-order rate constants (kR) for the reaction X + OH + He → XOH + He are thus compared: [graphic omitted]. Extrapolation of the rate data to flame conditions is considered with particular emphasis on the role of H2O as a third body in recombination reactions of this type. It is concluded that a reassessment of the standard collisional deactivation efficiency, βc, for H2O at elevated temperatures can be used to reconcile former differences between recombination rate data extrapolated from measurements of the present type with those derived from modelling on flames.

The excitation energy transfer processes in the rare gas-hydrogen chloride systems

The rare gas sensitized radiolysis of gaseous hydrogen chloride was performed, and the mechanism of the excitation transfer processes was investigated. It has been confirmed that at p R > 100 torr, the three body reactions (4) play the main role. The k 4 = 4.8 × 10 −28 cm 6 s −1 for R = Kr, Xe, and k 4 = 2.3 × 10 −28 cm 6 s −1 for R = Ar, as well as the relative rate constants of the collisional deactivation of the formed exciplex (RHCl) ∗ were obtained.

Laser induced fluorescence study of Xe(5p56p, 5p56p′, 5p57p, and 5p56d) states in Ne and Ar: Radiative lifetimes and collisional deactivation rate constants

The radiative lifetimes and the collisional deactivation constants by Ne and Ar for all 6p, 6p′, 7p, and 6d states of Xe, except two, were studied by single or two-photon laser induced fluorescence in the afterglow of a pulsed discharge [the prime symbol denotes the Xe+(2P1/2) core rather than the Xe+(2P3/2) core]. The radiative lifetimes, 30–48 ns for 6p and 6p′ states and 68–172 ns for 7p states, agree well with theoretical values; but, the agreement between experiment and theory is less satisfactory for the 6d states. The collisional deactivation constants for Ne and Ar are similar if there is a nearby product level. However, the deactivation constants by Ar are much larger than for Ne, if there is a large energy defect for the product state. The product distributions also were measured; Ar collisions give products with larger energy defect than collisions with Ne, which tend to favor nearly isoenergetic product states. The number and type of product channels are related to the locations of crossings in the Rg–Xe potential curves and the more attractive nature of Ar–Xe* vs Ne–Xe*. There is no clear favoring between intra- and intermultiplet product states of Xe*. The radiative cascading (6p′,7p)→(7s or 4d)→6p also was studied.

Collisional deactivation of potassium (52PJ) by molecular hydrogen. Identification of the primary quenching channel

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCollisional deactivation of potassium (52PJ) by molecular hydrogen. Identification of the primary quenching channelKing C. Lin, Alan M. Schilowitz, and John R. WiesenfeldCite this: J. Phys. Chem. 1984, 88, 26, 6670–6675Publication Date (Print):December 1, 1984Publication History Published online1 May 2002Published inissue 1 December 1984https://doi.org/10.1021/j150670a033RIGHTS & PERMISSIONSArticle Views25Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (748 KB) Get e-Alerts

Collisional deactivation of highly vibrationally excited molecules. Dynamics of the collision event

Classical trajectories are used to study microscopic details of collisions between argon atoms and highly excited methane molecules. Plots of orbital angular momentum, methane rotational angular momentum, and methane vibrational-rotational energy during the course of a collision reveal strong couplings between the Ar + CH4 relative degrees of freedom and the CH4 vibrational-rotational motion.

Collisional deactivation of vibrationally excited N+.2

Collisional deactivation of vibrationally excited N+.2 was investigated using a tandem ion cyclotron resonance spectrometer. Relative rates of deactivation produced by collisions with He, Ne, Kr, Xe, and O2 were determined with respect to N2. Absolute deactivation rate constants were then derived from the known N+.2 /N2 deactivation rate. These derived rate coefficients agree within experimental uncertainty with previous selected ion flow tube measurements. Comparison is made between vibrational deactivation in ion-neutral and neutral–neutral systems. In addition the vibrational energy dependence of the charge transfer rates between N+.2 and Kr, NO., O2, and CO2 was investigated. Significant enhancement of the Kr and NO reaction rates was observed.

Relaxation of the 1Δ g state in pure liquid oxygen and in liquid mixtures of 16O 2 and 18O 2

We calculated the transition probability for collisional deactivation of the 1Δ g state of O 2. The intersystem crossing transitions to the v = 2 and v = 3 vibrational levels of the electronic ground state are found to be dominant. The calculated ratio of the relaxation rate constants of the isotopes 18O 2 and 16O 2 is compared with the measured value (50 s −1/2.3 × 10 4 s −1) in the liquid phase at T = 77 K. The measured 1Δ g relaxation rate constants in liquid 16O 2– 18O 2 mixtures depend non-linearly on concentration. An explanation of the non-linear behaviour in terms of changes in the transition probability and the collision frequency in the mixtures is discussed.

The effect of temperature on the collisional deactivation of electronically excited CO +

Collisional quenching rates with helium as a collision partner have been obtained for selectively excited rovibronic levels of the A 2Π i state of CO + at T = 94.207 and 298 K. Data are reported for collision induced electronic transitions with various energy gaps and Franck-Condon factors. The rate constants are approximately two to three orders of magnitude larger than recently measured ground state diatomic ion vibrational relaxation rates. The effect of temperature for the different vibronic levels is qualitatively the same; the cross section increases as the temperature is lowered. The results are discussed in terms of collision complex models based on the attractive portion of the intermolecular potential curve.

Reply to comment on “kinetic models for the CH 4(ν 3) deactivation in CH 4CH 4 collisions” by T.F. Hunter

In our paper we analysed recently published results on CH 4(ν 3) collisional deactivation. The kinetic models developed in that paper have enabled us to interpret the results obtained by Avramides and Hunter (contrary to the assertion in Hunter's Comment). In any case: (1) we do not agree with the theoretical expressions used by Avramides and Hunter; (2) some of their results — as they themselves admit for Kba — seem “surprising” and are inconsistent with those obtained in our laboratory.

Collisional deactivation of vibrationally highly excited polyatomic molecules. IV. Temperature dependence of 〈ΔE〉.

The collisional loss of energy from vibrationally highly excited toluene molecules (excitation energy 52 000 cm−1) was monitored directly by time-resolved UV absorption spectroscopy after laser excitation. Experiments were performed in a variety of bath gases heated up to 870 K with a modulated cw CO2 laser. Comparison with experiments at 300 K yields information on the temperature dependence of the average energy 〈ΔE〉 transferred per collision. The temperature coefficient of 〈ΔE〉∝T n was found to be close to zero (n=0.0±0.2) for monoatomic and diatomic bath gases; for larger bath gases small negative n values were found (n=−0.3±0.3). The results confirm earlier experiments on the steady-state photoisomerization of cycloheptatriene which were reevaluated. They are in marked disagreement with recent conclusions on a strong decline of 〈ΔE〉 with increasing temperature.

Deductions from the master equation for chemical activation

The master equation for unimolecular decomposition and collisional deactivation of an energetic species A formed by chemical reaction was investigated. Particular attention was paid to the validity of the approximation of neglecting upward transitions, i.e., collisional transitions in which energy is added to A. Calculations of κa , the collision frequency ω times the ratio of the rate of decomposition of A to that of deactivation, were performed for the stepladder model for very large and very small ω and for the separable model for small ω. Neglect of upward transitions reduces κa. For the stepladder model the amount by which κa is reduced is greater for large ω than it is for small ω. It was also found that κa is more sensitive to changes in 〈Δε〉−, the average internal energy loss from A in deactivating collisions, when ω is small than it is when ω is large. Thus, when fitting computational results to experimental data, one derives a 〈Δε〉− which is too small if one neglects upward transitions, and the amount by which 〈Δε〉− is too small is considerably greater for large ω than it is for small ω. This result explains both qualitatively and semiquantitatively the discrepancies in 〈Δε〉−’s derived from stepladder model calculations of low pressure and high pressure κa’s for sec-butyl radicals in the presence of rare gas diluents.

The rare gas sensitized radiolysis of hydrogen chloride

The γ-radiolysis of hydrogen chloride in the presence of argon, krypton and xenon has been investigated. The experimental results have shown that the decomposition of hydrogen chloride in collision with the excited rare gas atoms is inefficient, most probably because excitation transfer occurs via (RHCl∗) complexes. Rate constant ratios of the collisional deactivation of these complexes have been evaluated. Reactions of the electron involved in the Xe-HCl system are discussed. It has been found that only part of the thermal electrons captured by HCl forms H 2 as a final product.

Effect of reactant-surface stretching on chemical laser performance

High-pressure DF chemical lasers use gas trip jets to increase the laser cavity reactant mixing rate. The trip jets can improve the laser efficiency by about 100% when compared to the laminar mixing value. It is postulated that the trip jets create a secondary flow which increases the mixing rate by stretching the contact surface between the reactant streams. The surface stretching rate can be described in terms of a strain rate s0. A qualitative explanation for the performance characteristics of trip-nozzle lasers is provided herein by developing flow and laser models which can define the effect of strain on the reactant burning rate and laser efficiency. Strain affects laser performance via a single parameter 7 = 2s0/kc, where kc is a characteristic collisional deactivation rate for the lasing specie. Strain levels of 7 = 2-3 appear to be consistent with trip nozzle data. The model also indicates the efficiency of low-pressure laminar mixing (7 = 0) lasers could be increased significantly for strain rate levels in the 7 = 3-5 range. Nomenclature BJ,B2,B3 = constants, B1=(p2/p1)B2 B3 defined by Eq. (19) Cj,C2,C3 = constants in gain equation, see Eq. (10) Dj,D2,D3 = constants, Dl =KI/K3,D2 =K2/K3 D = molecular dif fusivity fiJ2 ~ functions in amplifier solution, Eq. (22)

Laser-induced fluorescence studies of ion collisional excitation in a drift field: Rotational excitation of N+2 in helium

Initial results are presented for a new method of studying collisional excitation and deactivation processes of molecular ions. Translationally excited ions are prepared in the uniform electric field of a drift tube. Collisions with the inert buffer gas lead to rotational excitation (T-R). Laser-induced fluorescence (LIF) is used as a direct optical probe of the internal states of N+2 using the B 2Σ+u–X 2Σ+g transition at 391.4 nm. In this initial experiment, rotational excitation is observed for N+2 in collisions with helium at energies up to 0.054 eV (c.m.). The rotational state distribution can be described by a Boltzmann temperature corresponding to the center-of-mass collision energy, in good agreement with theory. Approximately ten collisions or less are required to obtain full equilibration of the rotational distribution. Applications of this new technique to the interpretation of ion–molecule reaction rates in drift tubes and to the study of ion-neutral energy transfer processes are discussed.

The effect of isotopic substitution on the collisional quenching of vibronically excited CO+

Rovibronic levels of the A 2Πi state for 12C16O+ and 13C16O+ have been selectively excited by a pulsed, tunable dye laser and their time resolved fluorescence obtained as a function of helium pressure. These ions are formed by reaction of neutral carbon monoxide with helium metastable atoms created in a dc discharge. Since 13CO+ has essentially the same potential energy curves as 12CO+, but differs primarily in its vibrational energy spacings, this experiment accentuates the role, in the collisional deactivation process, of the high lying ground state vibrational levels which are adjacent to the laser populated vibronic levels of the A 2Πi state. Quenching rates are determined for the v′=0, 1, and 2 levels which have relatively insignificant isotope shifts of a few wave numbers for the two isotopes. The difference in rates for the two isotopic ions demonstrates the importance of the positions for the high lying v″=10 and 11 ground state levels which have large isotope shifts of hundreds of wave numbers. A discussion of the deactivation process is given in terms of perturbations, Franck–Condon factors, energy gaps, and other considerations.