Frequency comb assisted ir measurements of H3+, H2D+ and D2H+ transitions

We present recent measurements of the fundamental transitions of H$_3^+$, H$_2$D$^+$ and D$_2$H$^+$\footnote{ P. Jusko, C. Konietzko, S. Schlemmer, O. Asvany, {\it J. Mol. Spec.} 319 (2016) 55} in a 4~K 22-pole trap\footnote{ O. Asvany, S. Brünken, L. Kluge, S. Schlemmer, {\it Appl. Phys. B} 114 (2014) 203} by action spectroscopic techniques. Either Laser Induced Inhibition of Cluster Growth (He attachment at T$\approx$4~K), endothermic reaction of H$_3^+$ with O$_2$, or deuterium exchange has been used as measurement scheme. We used a 3 $\mu$m optical parametric oscillator coupled to a frequency comb\footnote{ O. Asvany, J. Krieg, S. Schlemmer, {\it Rev. Sci. Instr.} 83 (2012) 093110} in order to achieve accuracy generally below 1 MHz. Five transitions of H$_3^+$, eleven of H$_2$D$^+$ and ten of D$_2$H$^+$ were recorder in our spectral range. We compare our H$_3^+$ results with two previous frequency comb assisted works\footnote{ J.N. Hodges, A.J. Perry, P.A. Jenkins, B.M. Siller, B.J. McCall, {\it J. Chem. Phys.} 139 (2013) 164201}\footnote{ H.-C. Chen, C.-Y. Hsiao, J.-L. Peng, T. Amano, J.-T. Shy, {\it Phys. Rev. Lett.} 109 (2012) 263002}. Moreover, accurate determination of the frequency allows us to predict pure rotational transitions for H$_2$D$^+$ and D$_2$H$^+$ in the THz range

Infrared action spectroscopy of doubly charged PAHs and their contribution to the aromatic infrared bands

The so-called aromatic infrared bands are attributed to emission of polycyclic aromatic hydrocarbons. The observed variations toward different regions in space are believed to be caused by contributions of different classes of PAH molecules, i.e. with respect to their size, structure, and charge state. Laboratory spectra of members of these classes are needed to compare them to observations and to benchmark quantum-chemically computed spectra of these species. In this paper we present the experimental infrared spectra of three different PAH dications, naphthalene$^{2+}$, anthracene$^{2+}$, and phenanthrene$^{2+}$, in the vibrational fingerprint region 500-1700~cm$^{-1}$. The dications were produced by electron impact ionization of the vapors with 70 eV electrons, and they remained stable against dissociation and Coulomb explosion. The vibrational spectra were obtained by IR predissociation of the PAH$^{2+}$ complexed with neon in a 22-pole cryogenic ion trap setup coupled to a free-electron infrared laser at the Free-Electron Lasers for Infrared eXperiments (FELIX) Laboratory. We performed anharmonic density-functional theory calculations for both singly and doubly charged states of the three molecules. The experimental band positions showed excellent agreement with the calculated band positions of the singlet electronic ground state for all three doubly charged species, indicating its higher stability over the triplet state. The presence of several strong combination bands and additional weaker features in the recorded spectra, especially in the 10-15~$\mu$m region of the mid-IR spectrum, required anharmonic calculations to understand their effects on the total integrated intensity for the different charge states. These measurements, in tandem with theoretical calculations, will help in the identification of this specific class of doubly-charged PAHs as carriers of AIBs.Comment: Accepted for publication in A&

H/D exchange in reactions of OH− with D2 and of OD− with H2 at low temperatures

Using a cryogenic linear 22-pole rf ion trap, rate coefficients for H/D exchange reactions of OH− with D2 (1) and OD− with H2 (2) have been measured at temperatures between 11 K and 300 K with normal hydrogen. Below 60 K, we obtained k1 = 5.5 × 10−10 cm3 s−1 for the exoergic reaction (1). Upon increasing the temperature above 60 K, the data decrease with a power law, k1(T) [similar] T−2.7, reaching ≈1 × 10−10 cm3 s−1 at 200 K. This observation is tentatively explained with a decrease of the lifetime of the intermediate complex as well as with the assumption that scrambling of the three hydrogen atoms is restricted by the topology of the potential energy surface. The rate coefficient for the endoergic reaction (2) increases with temperature from 12 K up to 300 K, following the Arrhenius equation, k2 = 7.5 × 10−11 exp(−92 K/T) cm3 s−1 over two orders of magnitude. The fitted activation energy, EA-Exp = 7.9 meV, is in perfect accordance with the endothermicity of 24.0 meV, if one accounts for the thermal population of the rotational states of both reactants. The low mean activation energy in comparison with the enthalpy change in the reaction is mainly due to the rotational energy of 14.7 meV contributed by ortho-H2 (J = 1). Nonetheless, one should not ignore the reactivity of pure para-H2 because, according to our model, it already reaches 43% of that of ortho-H2 at 100 K.Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

Plasma in electric and magnetic fields

Department of Surface and Plasma ScienceKatedra fyziky povrchů a plazmatuFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Astrochémia negatívnych iónov - Laboratórne štúdium

A B S T R A K T Predložená práca sa zaoberá experimentálnym štúdiom interakcie an- iónov s neutrálnymi časticami pri teplotách relevantných pre astro- fyziku. Zaoberali sme sa aniónom H− , doležitým pri tvorbe moleku- lárneho vodíka a aniónom O− , ako možným zdrojom vody. Určili sme teplotnú závislost' rýchlostného koeficientu reakcie v rozmedzí teplôt 10 až 150 K pre reakcie H− + H → H2 + e− a O− + H2 → H2O + e−. Získali sme rozdelenie energií elektrónov produkovaných v druhej z menovaných reakcií pri teplote 300 K. Merania prebiehali na dvoch ex- perimentálnych zariadeniach, v práci uvádzame ich princíp činnosti, konštrukciu, kalibráciu a podporné merania.A B S T R A C T Presented work focuses on experimental study of anion interaction with neutral particles at temperatures relevant for astrophysics. Anion H− , important for molecular hydrogen creation, and O− as a possible source of water are investigated. The temperature dependence of reac- tion rate coefficients from 10 to 150 K for reactions H− + H → H2 + e− and O− + H2 → H2O + e− has been determined. The energy distri- bution of electrons produced in the latter reaction at 300 K has also been acquired. These studies have been performed on two experimen- tal setups, which are presented together with the theory of operation, construction details, calibration, and supporting test measurements.Department of Surface and Plasma ScienceKatedra fyziky povrchů a plazmatuFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Application of evolutionary modelling in physics

Katedra fyziky povrchů a plazmatuDepartment of Surface and Plasma ScienceFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Negative Ion Astrochemistry - a Laboratory Study

A B S T R A C T Presented work focuses on experimental study of anion interaction with neutral particles at temperatures relevant for astrophysics. Anion H− , important for molecular hydrogen creation, and O− as a possible source of water are investigated. The temperature dependence of reac- tion rate coefficients from 10 to 150 K for reactions H− + H → H2 + e− and O− + H2 → H2O + e− has been determined. The energy distri- bution of electrons produced in the latter reaction at 300 K has also been acquired. These studies have been performed on two experimen- tal setups, which are presented together with the theory of operation, construction details, calibration, and supporting test measurements

Double resonance rotational spectroscopy of CH

Context. Deuterated forms of CH3+ are thought to be responsible for deuterium enrichment in lukewarm astronomical environments. There is no unambiguous detection of CH2D+ in space to date. Aims. Four submillimetre rotational lines of CH2D+ are documented in the literature. Our aim is to present a complete dataset of highly resolved rotational lines, including millimetre (mm) lines needed for a potential detection. Methods. We used a low-temperature ion trap and applied a novel IR–mm-wave double resonance method to measure the rotational lines of CH2D+. Results. We measured 21 low-lying (J ≤ 4) rotational transitions of CH2D+ between 23 GHz and 1.1 THz with accuracies close to 2 ppb

Frequency comb assisted measurement of fundamental transitions of cold H-3(+), H2D+ and D2H+

HI and two of its deuterated variants have been trapped and cooled in a 4K trap machine, and their fundamental vibrational transitions probed with the laser induced reactions method. With the help of a frequency comb system the line centers are determined with high accuracy and precision, typically well below 1 MHz. For the deuterated variants, ground state combination differences allow for comparison with existing rotational THz data, and the accurate prediction thereof. (C) 2015 Elsevier Inc. All rights reserved