Ternary Recombination Research Articles

Ternary recombination of excited Ar+(P1/22) ions, established experimental results reinterpreted with a new extended model.

For many years, the recombination of excited ions of argon, Ar+(P1/22), has been assumed negligible under ambient conditions as compared to the recombination of ground-state ions, Ar+(P3/22). This opinion was confronted with detailed experimental results that seem to clearly support it. Here, we propose a new interpretation in light of our recent calculations, which shows that the recombination efficiency is comparable for both fine-structure states. Noteworthily, in our model leading to a picture consistent with the experiment, residual dimer ions emerge from Ar+(P1/22) due to non-adiabatic dynamics effects and interplay in measured data.

Formation of Ar2+ ions in cold argon plasmas through the ternary recombination mechanism

A general scheme for calculating ternary recombination rate constants of atomic species based on a hybrid quantum–classical nonadiabatic dynamics approach is presented and applied to the specific case of the ternary recombination of atomic ions of argon in cold argon plasmas. Rate constants are reported for both fine-structure states of the Ar+ ion, 2P3/2 and 2P1/2 , T = 300 K, and for selected values of the reduced electric field. A thorough comparison with the literature data available for T = 300 K and a couple of close temperatures is performed with a favorable agreement achieved. It is shown that the excited Ar+(2P1/2) ions may contribute to the formation of dimer ions, Ar2+ , as efficiently as the ground-state ions, Ar+(2P3/2) , due to fast internal conversion of the electronic energy, which takes place in ternary collision complexes, Ar+/Ar/Ar .

Cavity ring-down spectroscopy study of neon assisted recombination of [formula omitted] ions with electrons

A stationary afterglow apparatus with Cavity Ring-Down spectrometer was combined with electron number density measurement system to study the third-body assisted recombination of H3+ ions with electrons in neon gas at the temperature of 110 K. The measured ternary recombination rate coefficient KNe(110K)=(1.8±0.2)×10-25cm6s-1 is close to that obtained in helium buffered plasma. The applicability of the present experimental setup for Einstein coefficients determination is also discussed.

Electron-ion recombination in low temperature hydrogen/deuterium plasma

The stationary afterglow with cavity ring down spectrometer (SA-CRDS) was used to study the recombination of H3 + , H2 D+ , HD2 + and D3 + ions with electrons in low temperature (77–300 K) plasmas in He/Ar/H2 /D2 gas mixtures. By measuring effective recombination rate coefficients (α eff ) in plasma with mixtures of ions and their dependences on temperature and partial densities of He, H2 and D2 , α eff (T , [He],[H2 ],[D2 ]), we determined binary (α binH3 , α binH2D , α binHD2 , α binD3 ) and ternary (K H3 , K H2D , K HD2 , K D3 ) recombination rate coefficients for H3 + , H2 D+ , HD2 + and D3 + ions. For all four ions we observed very efficient He assisted ternary recombination which is comparable with binary recombination already at [He] =1 × 1017 cm−3 . The removal of excited particles in afterglow plasma was monitored to obtain the plasma thermalisation rate at given experimental conditions. The inferred deexcitation rates for reaction of helium metastable atoms with D2 are k D2 (300 K)=(2.1 ± 0.3) × 10−10 cm3 s−1 and k D2 (140 K)=(1.3 ± 0.3) × 10−10 cm3 s−1 .

Stationary afterglow measurements of the temperature dependence of the electron–ion recombination rate coefficients of and in He/Ar/H2/D2 gas mixtures at T = 80–145 K

We report measurements of the binary and ternary recombination rate coefficients of deuterated isotopologues of . A cavity ring-down absorption spectrometer was used to monitor the fractional abundances of , , and during the decay of a plasma in He/Ar// mixtures. A dependence of the measured effective recombination rate coefficients on the helium buffer gas density was observed and hence both the binary and the ternary recombination rate coefficients for and were obtained in the temperature range 80–145 K.

Reactive two-body and three-body collisions ofBa+in an ultracold Rb gas

We analyze reactive collisions of a single Ba$^+$ ion in contact with an ultracold gas of Rb atoms at low three-body collision energies of 2.2(9) mK$\times k_{\mathrm{B}}$. Mapping out the Ba$^+$ loss rate dependence on the Rb atom density we can discern two-body reactive collisions from three-body ones and for the first time determine both rate coefficients which are $k_2=3.1(6)(6)\times 10^{-13}\textrm{cm}^{3}\textrm{s}^{-1}$ and $k_3=1.04(4)(45)\times 10^{-24}\textrm{cm}^{6}\textrm{s}^{-1}$, respectively (statistical and systematic errors in parenthesis). Thus, the measured ternary recombination dominates over binary reactions even at moderate atom densities of $n\approx 10^{12}\: \textrm{cm}^{-3}$. The results for Ba$^+$ and Rb are representative for a wide range of cold ion-atom systems and can serve as a guidance for the future development of the field of hybrid atom-ion research.

Chromatin architecture may dictate the target site for DMC1, but not for RAD51, during homologous pairing.

In eukaryotes, genomic DNA is compacted as chromatin, in which histones and DNA form the nucleosome as the basic unit. DMC1 and RAD51 are essential eukaryotic recombinases that mediate homologous chromosome pairing during homologous recombination. However, the means by which these two recombinases distinctly function in chromatin have remained elusive. Here we found that, in chromatin, the human DMC1-single-stranded DNA complex bypasses binding to the nucleosome, and preferentially promotes homologous pairing at the nucleosome-depleted regions. Consistently, DMC1 forms ternary complex recombination intermediates with the nucleosome-free DNA or the nucleosome-depleted DNA region. Surprisingly, removal of the histone tails improperly enhances the nucleosome binding by DMC1. In contrast, RAD51 does not specifically target the nucleosome-depleted region in chromatin. These are the first demonstrations that the chromatin architecture specifies the sites to promote the homologous recombination reaction by DMC1, but not by RAD51.

H2-assisted ternary recombination ofH3+with electrons at 300 K

Stationary afterglow measurements in conjunction with near-infrared absorption spectroscopy show that the recombination of the ${\text{H}}_{3}{}^{+}$ ion with electrons in ionized gas mixtures of He, Ar, and ${\text{H}}_{2}$ at 300 K is strongly enhanced by neutral helium and by molecular hydrogen. The ${\text{H}}_{2}$-assisted ternary recombination coefficient ${K}_{{\text{H}}_{2}}=(8.7\ifmmode\pm\else\textpm\fi{}1.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}23}\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{6}{\text{s}}^{\ensuremath{-}1}$ substantially exceeds the value measured for ${\text{H}}_{3}{}^{+}$ in ambient helium $({K}_{\mathrm{He}}\ensuremath{\sim}{10}^{\ensuremath{-}25}\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{6}\phantom{\rule{0.16em}{0ex}}{\text{s}}^{\ensuremath{-}1})$ or predicted by the generally accepted classical theory of Bates and Khare $(\ensuremath{\sim}{10}^{\ensuremath{-}27}\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{6}\phantom{\rule{0.16em}{0ex}}{\text{s}}^{\ensuremath{-}1})$ for atomic ions. Because of the extremely large value of ${K}_{{\text{H}}_{2}}$ in a hydrogen plasma the ternary recombination dominates over binary recombination already at pressures above 3 Pa. This can have consequences in plasma physics, astrophysics, recombination pumped lasers, plasma spectroscopy, plasmatic technologies, etc. The ternary processes provide a plausible explanation for the discrepancies between many earlier experimental results on ${\text{H}}_{3}{}^{+}$ recombination. The observation that the ternary process saturates at high He and ${\text{H}}_{2}$ densities suggests that recombination proceeds by a two-step process: formation of a long-lived complex [with a rate coefficient ${\ensuremath{\alpha}}_{\mathrm{F}}=(1.5\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{3}\phantom{\rule{0.16em}{0ex}}{\text{s}}^{\ensuremath{-}1}]$ followed by collisional stabilization.

Collisional-radiative recombination of Ar+ions with electrons in ambient helium at temperatures from 50 K to 100 K

Ternary electron-assisted collisional radiative recombination (E-CRR) and neutral-assisted radiative recombination (N-CRR) have very strong negative temperature dependencies and hence dominate electron recombination in some plasmas at very low temperatures. However, there are only few data for molecular ions and almost none for atomic ions at temperatures much below 300 K. In this experimental study we used a cryogenic afterglow plasma experiment (Cryo-FALP II) at temperatures from 50 K to 100 K to measure ternary recombination rate coefficients for ${\mathrm{Ar}}^{+}$ ions in ambient helium gas. The measured magnitudes and the temperature dependencies of the ternary recombination rate coefficients for electron-assisted and neutral-assisted collisional radiative recombination agree well with theoretical predictions (${K}_{\mathrm{E}\ensuremath{-}\mathrm{CRR}}\ensuremath{\sim}{T}^{\ensuremath{-}4.5}$ and ${K}_{\mathrm{He}\ensuremath{-}\mathrm{CRR}}\ensuremath{\sim}{T}^{\ensuremath{-}2.5}$ to ${T}^{\ensuremath{-}2.9}$) over a broad range of electron and He densities.

Ternary Recombination of H3+ and D3+ with Electrons in He–H2 (D2) Plasmas at Temperatures from 50 to 300 K

We present results of plasma afterglow experiments on ternary electron-ion recombination rate coefficients of H3(+) and D3(+) ions at temperatures from 50 to 300 K and compare them to possible three-body reaction mechanisms. Resonant electron capture into H3* Rydberg states is likely to be the first step in the ternary recombination, rather than third-body-assisted capture. Subsequent interactions of the Rydberg molecules with ambient neutral and charged particles provide the rate-limiting step that completes the recombination. A semiquantitative model is proposed that reconciles several previously discrepant experimental observations. A rigorous treatment of the problem will require additional theoretical work and experimental investigations.

Binary and ternary recombination of ${\rm D}_3^+$D3+ ions at 80–130 K: Application of laser absorption spectroscopy

Recombination of D(3)(+) ions with electrons at low temperatures (80-130 K) was studied using spectroscopic determination of D(3)(+) ions density in afterglow plasmas. The use of cavity ring-down absorption spectroscopy enabled an in situ determination of the abundances of the ions in plasma and the translational and the rotational temperatures of the recombining ions. Two near infrared transitions at (5792.70 ± 0.01) cm(-1) and at (5793.90 ± 0.01) cm(-1) were used to probe the number densities of the lowest ortho state and of one higher lying rotational state of the vibrational ground state of D(3)(+) ion. The results show that D(3)(+) recombination with electrons consists of the binary and the third-body (helium) assisted process. The obtained binary recombination rate coefficients are in agreement with a recent theoretical prediction for electron-ion plasma in thermodynamic equilibrium with α(bin)(80 K) = (9.2 ± 2.0) × 10(-8) cm(3) s(-1). The measured helium assisted ternary rate coefficients K(He) are in agreement with our previously measured flowing afterglow data giving a value of K(He)(80 K) = (1.2 ± 0.3) × 10(-25) cm(6) s(-1).

Binary and ternary recombination of para-${\rm H}_3^+$H3+ and ortho-${\rm H}_3^+$H3+ with electrons: State selective study at 77–200 K

Measurements in H(3)(+) afterglow plasmas with spectroscopically determined relative abundances of H(3)(+) ions in the para-nuclear and ortho-nuclear spin states provide clear evidence that at low temperatures (77-200 K) para-H(3)(+) ions recombine significantly faster with electrons than ions in the ortho state, in agreement with a recent theoretical prediction. The cavity ring-down absorption spectroscopy used here provides an in situ determination of the para/ortho abundance ratio and yields additional information on the translational and rotational temperatures of the recombining ions. The results show that H(3)(+) recombination with electrons occurs by both binary recombination and third-body (helium) assisted recombination, and that both the two-body and three-body rate coefficients depend on the nuclear spin states. Electron-stabilized (collisional-radiative) recombination appears to make only a small contribution.

Cryo-FALP study of collisional-radiative recombination of Ar+ions at 40–200 K

New flowing afterglow apparatus, Cryo-FALP, was built to study ternary Collisional-Radiative Recombination (CRR) of Ar + ions with electrons in He/Ar afterglow plasma at temperatures 40-200 K. The obtained ternary recombination rate coefficient at 57 K is KCRR =( 3±1)×10 �17 cm 6 s �1 . It is the first time that the KCRR was measured below 77 K. The measured temperature dependence KCRR ∼ T (�4.5±0.4) is in a good agreement with theoretical prediction.

Recombination in low temperature Ar+ dominated plasmas

The results of measurements in low temperature Ar+ dominated afterglow plasmas are presented. The study was realized using Cryo-FALP apparatus operable in temperature range 77 – 300 K and at pressures 200 – 2000 Pa. We have observed decay of electron number density due to collisional radiative recombination (CRR). The measured ternary recombination rate coefficient of CRR of Ar+ ions with electrons and its temperature dependence are in good agreement with theoretical predictions of T −4.5 dependence.

Polynomial identities for ternary intermolecular recombination

The operation of binary intermolecular recombination, originating in the theory of DNAcomputing, permits a natural generalization to $n$-ary operations which performsimultaneous recombination of $n$ molecules. In the case $n = 3$, we use computeralgebra to determine the polynomial identities of degree $\le 9$ satisfied by this trilinearnonassociative operation. Our approach requires computing a basis for the nullspace ofa large integer matrix, and for this we compare two methods: the row canonical form, andthe Hermite normal form with lattice basis reduction. In the conclusion, we formulatesome conjectures for the general case of $n$-ary intermolecular recombination.

Binary and ternary recombination of and ions with electrons in low temperature plasma

Measurements of recombination rate coefficients of binary and ternary recombination of and ions with electrons in a low temperature plasma are described. The experiments were carried out in the afterglow plasma in helium with a small admixture of Ar and parent gas (H2 or D2). For both ions a linear increase of measured apparent binary recombination rate coefficients (αeff) with increasing helium density was observed: αeff = αBIN + K He[He]. From the measured dependencies, we have obtained for both ions the binary (αBIN) and the ternary (K He) rate coefficients and their temperature dependence. For the description of observed ternary recombination a mechanism with two subsequent rate determining steps is proposed. In the first step, in + e− (or + e−) collision, a rotationally excited long-lived Rydberg molecule (or ) is formed. In the following step (or ) collides with a He atom of the buffer gas and this collision prevents autoionization of (or ). Lifetimes of the formed (or ) and corresponding ternary recombination rate coefficients have been calculated. The theoretical and measured binary and ternary recombination rate coefficients obtained for and ions are in good agreement.

Temperature dependence of binary and ternary recombination of D3+ ions with electrons

Flowing and stationary afterglow experiments were performed to study the recombination of D(3)(+) ions with electrons at temperatures from 77 to 300 K. A linear dependence of apparent (effective) binary recombination rate coefficients on the pressure of the helium buffer gas was observed. Binary (D(3)(+)+e(-)) and ternary (D(3)(+)+e(-)+He) recombination rate coefficients were derived. The obtained binary rate coefficient agrees with recent theoretical values for dissociative recombination of D(3)(+). We describe the observed ternary process by a mechanism with two rate determining steps. In the first step, a rotationally excited long-lived neutral D(3)* is formed in D(3)(+)-e(-) collisions. As the second step, the D(3)* collides with a helium atom that prevents autoionization of D(3)*. We calculate lifetimes of D(3)* formed from ortho-, para-, or metastates of D(3)(+) and use the lifetimes to calculate ternary recombination rate coefficients.

Application of NIR – CRDS for state selective study of recombination of para and ortho H3+ ions with electrons in low temperature plasma

We present a study of H3+ recombination performed at 77 K on the two lowest rotational levels of this ion, which belong to its two different nuclear spin states of the studied ion. A near infrared cavity ring-down spectrometer (~1381 nm, CRDS arrangement) has been used to obtain the time evolution of concentration of both states. From the overall ion density decay during the afterglow we obtained the binary recombination rate coefficient αbin (77 K) = 1.2×10−7 cm3s−1. We have also observed ternary helium assisted recombination of both para and ortho H3+. The process is very slow (at 77 K) and the obtained ternary recombination rate coefficient is in contradiction with the theoretical prediction. It is the first time that the binary and ternary H3+ recombination rate coefficient was measured at a known population of para and ortho H3+ ions in decaying plasma.

Binary and ternary recombination ofD3+ions with electrons inHe-D2plasma

An experimental study is reported about the recombination of $\text{D}_{3}{}^{+}$ ions with electrons in a low-temperature plasma (200--300 K) consisting of He with a small admixture of ${\text{D}}_{2}$. At several temperatures, the pressure dependence of the apparent binary recombination rate coefficient $({\ensuremath{\alpha}}_{\text{eff}})$ was measured over a broad range of helium pressures (200--2000 Pa). The binary and ternary recombination rate coefficients were obtained from measured pressure dependences of ${\ensuremath{\alpha}}_{\text{eff}}$. The binary recombination rate coefficient obtained ${\ensuremath{\alpha}}_{\text{bin}}(300\text{ }\text{K})=(2.7\ifmmode\pm\else\textpm\fi{}0.9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\text{ }{\text{cm}}^{3}\text{ }{\text{s}}^{\ensuremath{-}1}$ is in agreement with recent theory. The ternary recombination rate coefficient obtained is ${K}_{\text{He}}(300\text{ }\text{K})=(1.8\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}\text{ }{\text{cm}}^{6}\text{ }{\text{s}}^{\ensuremath{-}1}$. In analogy with the recently described process of helium-assisted ternary recombination of $\text{H}_{3}{}^{+}$ ions, it is suggested that the ternary helium-assisted recombination of $\text{D}_{3}{}^{+}$ ions proceeds through the formation of a neutral long-lived highly excited Rydberg molecule ${\text{D}}_{3}$ followed by a collision with a He atom.

Temperature dependence of binary and ternary recombination ofH3+ions with electrons

We study binary and the recently discovered process of ternary He-assisted recombination of H3+ ions with electrons in a low temperature afterglow plasma. The experiments are carried out over a broad range of pressures and temperatures of an afterglow plasma in a helium buffer gas. Binary and He-assisted ternary recombination are observed and the corresponding recombination rate coefficients are extracted for temperatures from 77 K to 330 K. We describe the observed ternary recombination as a two-step mechanism: First, a rotationally-excited long-lived neutral molecule H3* is formed in electron-H3+ collisions. Second, the H3* molecule collides with a helium atom that leads to the formation of a very long-lived Rydberg state with high orbital momentum. We present calculations of the lifetimes of H3* and of the ternary recombination rate coefficients for para and ortho-H3+. The calculations show a large difference between the ternary recombination rate coefficients of ortho- and para-H3+ at temperatures below 300 K. The measured binary and ternary rate coefficients are in reasonable agreement with the calculated values.