Luminescence spectroscopy of matrix-isolated z 6P state atomic manganese

The relaxation of electronically excited atomic manganese isolated in solid rare gas matrices is observed from recorded emission spectra, to be strongly site specific. z 6P state excitation of Mn atoms isolated in the red absorption site in Ar and Kr produces narrow a 4D and a 6D state emissions while blue-site excitation produces z 6P state fluorescence and broadened a 4D and a 6D emissions. MnXe exhibits only a single thermally stable site whose emission at 620 nm is similar to the broad a 6D bands produced with blue-site excitation in Ar and Kr. Thus in Ar(Kr), excitation of the red site at 393 (400) nm produces narrow line emissions at 427.5 (427.8) and 590 (585.7) nm. From their spectral positions, linewidths, and long decay times, these emission bands are assigned to the a 4D72 and a 6D92 states, respectively. Excitation of the blue site at 380 (385.5) nm produces broad emission at 413 (416) nm which, because of its nanosecond radiative lifetime, is assigned to resonance z 6P --> a 6S fluorescence. Emission bands at 438 (440) and 625 (626.8) nm, also produced with blue-site excitation, are broader than their red-site equivalents at 427.5 and 590 nm (427.8 and 585.7 nm in Kr) but from their millisecond and microsecond decay times are assigned to the a 4D and a 6D states. The line features observed in high resolution scans of the red-site emission at 427.5 and 427.8 nm in MnAr and MnKr, respectively, have been analyzed with the W(p) optical line shape function and identified as resolved phonon structure originating from very weak (S=0.4) electron-phonon coupling. The presence of considerable hot-phonon emission (even in 12 K spectra) and the existence of crystal field splittings of 35 and 45 cm(-1) on the excited a 4D72 level in Ar and Kr matrices have been identified in W(p) line shape fits. The measured matrix lifetimes for the narrow red-site a 6D state emissions (0.29 and 0.65 ms) in Ar and Kr are much shorter than the calculated (3 s) gas phase value. With the lifetime of the metastable a 6D92 state shortened by four orders of magnitude in the solid rare gases, it is clear that the probability of the "forbidden" a 6D --> a 6S atomic transition is greatly enhanced in the solid state. A novel feature identified in the present work is the large width and shifted 4D and 6D emissions produced for Mn atoms isolated in the blue sites of Ar and Kr. In contrast, these states produce narrow, unshifted (gas-phase-like) 4D and 6D state emissions from the red site.     

Photodissociation of formyl fluoride in rare gas matrixes

Photodissociation of formyl fluoride (HCOF) is studied in Ar, Kr, and Xe matrixes at 248 and 193 nm excitation by following spectral changes in the infrared absorption spectra. In all matrixes, the main photodissociation products are CO/HF species, including CO-HF and OC-HF complexes and thermally unstable CO/HF species (a distorted CO/HF complex or a reaction intermediate), which indicate negligible cage exit of atoms produced via the C-F and C-H bond cleavage channels. However, the observation of traces of H, F, CO, CO(2), F(2)CO, FCO, and HRg(2)(+) (Rg = Kr or Xe) in Kr and Xe matrixes would imply some importance of other reaction channels too. The analysis of the decay curves of the precursor shows that dissociation efficiency of HCOF increases as Ar < Kr < Xe, the difference being the factor of 10 between Ar and Xe. Moreover, HCOF dissociates 20-50 times faster at 193 nm compared to 248 nm. Interestingly, whereas the CO/HF species are stable with respect to photolysis in Ar, they photobleach in Kr and Xe matrixes at 248 and 193 nm, even though the first excited states of CO and HF are not energetically accessible with 193 and 248 nm photons. In krypton matrix, the photodissociation of CO/HF species at 248 nm is observed to be a single photon process. Quantum chemical calculations of electronic excitation energies of CO-HF and OC-HF complexes show that the electronic states of HF and CO mostly retain their diatomic nature in the pair. This clearly demonstrates that photodissociation of CO/HF complexes is promoted by the surrounding rare gas lattice.     

Radiative and nonradiative lifetimes in excited states of Ar,Kr and Xe atoms in a neon matrix

Synchrotron radiation with its intense continuum and its excellent time structure has been exploited for time resolved luminescence spectroscopy in the solid state. By selective excitation of n = 1, n′ = 2 exciton states of Xe, Kr and Ar atoms in a neon matrix we were able to identify the emitting states involved. Lifetimes within the cascade of radiative and radiationless relaxation between excited states as well as the radiative lifetimes for transitions to the ground state have been derived from the decay curves. Energy positions and radiative lifetimes of the emitting states correspond quite well with those of the free atoms. Radiative and radiationless relaxation processes take place within the manifold of excited states of the guest atoms. The rate constants for radiationless decay confirm an energy gap law. The order of the radiationless processes reaches in some cases extremely high values. Selection rules for spin and angular momentum are essential to understand the observed radiationless transition rates.     

Dissociation processes of Kr2(+) and Kr3(+) studied by threshold photoelectron-photoion coincidence measurements

A time-of-flight (TOF) ion mass spectrum in coincidence with threshold photoelectrons was measured in the photon energy region between the first and second dissociation limits of Kr2(+) to examine the decay processes of the Kr2(+) II(1/2u) state. The measured TOF spectrum reveals that Kr+ fragment ions are produced through dissociation of the repulsive I(1/2g) state, which can be formed by the decay process of the II(1/2u) state accompanied with emission of photons. The potential-energy curve of the I(1/2g) state is deduced with detailed analysis of the observed TOF spectrum, in which the radiative lifetime of the II(1/2u) state was also derived to be 2.5 micros. Additionally, evidence of the dissociation process of Kr3(+) ions was obtained in the same photon energy region, where the dominant channel is Kr3(+) --> Kr2(+) + Kr.     

Electronic spectroscopy of I(2)-Xe complexes in solid Krypton

In the present work, we have studied ion-pair states of matrix-isolated I(2) with vacuum-UV absorption and UV-vis-NIR emission, where the matrix environment is systematically changed by mixing Kr with Xe, from pure Kr to a more polarizable Xe host. Particular emphasis is put on low doping levels of Xe that yield a binary complex I(2)-Xe, as verified by coherent anti-Stokes Raman scattering (CARS) measurements. Associated with interaction of I(2) with Xe we can observe strong new absorption in vacuum-UV, redshifted 2400 cm(-1) from the X → D transition of I(2). Observed redshift can be explained by symmetry breaking of ion-pair states within the I(2)-Xe complex. Systematic Xe doping of Kr matrices shows that at low doping levels, positions of I(2) ion-pair emissions are not significantly affected by complexation with Xe, but simultaneous increase of emissions from doubly spin-excited states indicates non-radiative relaxation to valence states. At intermediate doping levels ion-pair emissions shift systematically to red due to change in the average polarizability of the environment. We have conducted spectrally resolved ultrafast pump-probe ion-pair emission studies with pure and Xe doped Kr matrices, in order to reveal the influence of Xe to I(2) dynamics in solid Kr. Strikingly, relaxed emission from the ion-pair states shows no indication of complex presence. It further indicates that the complex escapes detection due to a non-radiative relaxation.     

Simulation of vibrational dephasing of I(2) in solid Kr using the semiclassical Liouville method

In this paper, we present simulations of the decay of quantum coherence between vibrational states of I(2) in its ground (X) electronic state embedded in a cryogenic Kr matrix. We employ a numerical method based on the semiclassical limit of the quantum Liouville equation, which allows the simulation of the evolution and decay of quantum vibrational coherence using classical trajectories and ensemble averaging. The vibrational level-dependent interaction of the I(2)(X) oscillator with the rare-gas environment is modeled using a recently developed method for constructing state-dependent many-body potentials for quantum vibrations in a many-body classical environment [J. M. Riga, E. Fredj, and C. C. Martens, J. Chem. Phys. 122, 174107 (2005)]. The vibrational dephasing rates gamma(0n) for coherences prepared between the ground vibrational state mid R:0 and excited vibrational state mid R:n are calculated as a function of n and lattice temperature T. Excellent agreement with recent experiments performed by Karavitis et al. [Phys. Chem. Chem. Phys. 7, 791 (2005)] is obtained.     

Protons solvated in noble-gas matrices: interaction with nitrogen

The interaction of a (NgHNg)(+) cation (Ng = Ar and Kr) with a nitrogen molecule is studied. The structure, energetics, and vibrational properties of these complexed systems are computationally studied at the MP2/6-311++G(2d,2p) level of theory. The computations reveal two stable structures, linear and T-shaped configurations, with BSSE corrected interaction energies of the order of -1000 cm(-1). The (NgHNg)(+)[dot dot dot]N(2) complexes are characterized experimentally by IR absorption spectroscopy in solid Ar and Kr matrices. The spectra show that only one complex structure is present, as evidenced by the single nitrogen-induced nu(3) band. According to the computational results, the linear structure is more probable in the experiments. However, our results show that the one-to-one complex at the present computational level does not accurately agree with the matrix-isolation experiments, the differences originating possibly from the influence of the surrounding matrix. Based on the current data, the mechanism of cation decay in noble-gas matrices is discussed. The observed similar decay of (NgHNg)(+) and its N(2) complex indicates that the solvated proton is unable to tunnel and is therefore immobile in noble-gas matrices. The observations for the cation decay are consistent with the electron neutralization mechanism.     

Modelization of the fragmentation dynamics of krypton clusters (Kr(n),n=2-11) following electron impact ionization

We present the first prediction for the fragmentation dynamics following electron impact ionization of neutral krypton clusters from 2 to 11 atoms. Fragment proportions and parent ion lifetimes are deduced from a molecular dynamics with quantum transitions study in which the nuclei are treated classically and the transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model to which induced dipole-induced dipole and spin-orbit interactions are added. The results show surprisingly fast and extensive fragmentation for clusters of such a heavy atom, although not as extensive as in the case of neon clusters studied previously [D. Bonhommeau et al., J. Chem. Phys. 123, 54316 (2005)]. The parent ion lifetimes range from 2.8 to 0.7 ps, and the most abundant fragment is Kr(2) (+) for all studied sizes, followed by Kr(+) for sizes smaller than 7 atoms and by Kr(3) (+) for larger sizes. Trimer and larger fragments are found to originate from the lower electronic states of parent ions. The comparison with preliminary results from experiments on size-selected neutral clusters conducted by Steinbach et al. (private communication) reveal a good agreement on the extensive character of the fragmentation. It is checked that the additional internal energy brought by the helium scattering technique used for size selection does not affect the fragment proportions. In addition, the existence of long-lived trajectories is revealed, and they are found to be more and more important for larger cluster sizes and to favor the stabilization of larger fragments. The implications of this work for microsecond-scale dynamics of ionized rare-gas clusters are discussed. In particular, given the extent of fragmentation of the parent clusters and the fast kinetics of the whole process, the small cluster ions that exhibit a monomer loss in the microsecond time window must originate from much larger neutral precursors. The decay rate of the II(12)(u) state of the ionic dimer Kr(2) (+) by spin-orbit coupling is found to be of the order of 3 ps, in contrast to the expected tens of microseconds, but only reasonably faster than the corresponding state of HeNe(+). Finally, the spin-orbit interaction strongly affects both the Kr(+)Kr(2) (+) ratio and some of the characteristic times of the dynamics, especially for smaller sizes, but not the overall dependence of the fragment proportions as a function of cluster size.     

Gaunt factors for free-free transitions in the fields of the first ions of the rare gases,calculated in the scaled Thomas-Fermi approximation

The Scaled Thomas-Fermi method is adapted to the case of positive energy states and used for the calculation of free-free transition probabilities and the corresponding temperature-averaged Gaunt factors of Ne I, Ar I, Kr I, and Xe I. The results are compared with those of the single-channel quantum defect method.     

Kr对HF(X1Σ+)基频和泛频的影响

运用Monte-Carlo轨迹法研究了Kr(1Sg)+HF(X1Σ+;ν=1,2,3;J=4)→Kr(1Sg)+HF(X1Σ+,ν',J')的碰撞过程,从而分析Kr原子对HF基频和泛频的影响。研究表明：在初始相对平动能Et≤251.0kJ/mol时,Kr原子能够减少产生基频的粒子数反转,增加产生泛频特别是ν'=2能级的粒子数反转,并且,Kr原子有较强的弛豫高转动态（J'≥4）的能力,因此,Kr原子对HF泛频激光在提高光强和增强大气传输能力方面均有 较大的改善。     

Theoretical Study of Decomposition Pathways for Rare-gas-containing Compounds HRgX （Rg = He, Ne, Ar, Kr; X = Cl, Br）

1 INTRODUCTION transfer species with common formula H-Rgδ -Xδ, where X represents a strongly electrone-gative atom Since xenon hexafluoraplatinate, XePtF6 , the [1] or fragment, and Rg is a rare-gas atom. These species first rare gas-containing compound was discovered have linear equi- librium geometries and are mainly by Bartlett in 1962, rare gases are getting more and bound up by strong columbic attraction between (H- more attention and have been found to be possible to Rg) and…     

Ab initio study of the KrH+ photodissociation

The multireference spin-orbit configuration interaction method is employed to calculate potential energy curves for the ground and low-lying excited states of the KrH(+) cation. For the first time, the spin-orbit interaction is taken into account and electric dipole moments are computed for transitions to the states responsible for the first absorption continuum (A band) of KrH(+). On this basis, the partial and total absorption spectra in this energy range are obtained. It is shown that the A-band absorption is dominated by the parallel A (1)Sigma(+)<--X (1)Sigma(+) transition. In the low-energy part of the band (<83x10(3) cm(-1)) the absorption is mainly caused by the spin-forbidden b (3)Pi(0(+) )<--X (1)Sigma(+) excitation, while perpendicular transitions to the B (1)Pi and b (3)Pi(1) states are significantly weaker. The branching ratio Gamma for the photodissociation products is calculated and it is shown to increase smoothly from 0 in the red tail of the band to 1 at E>or=90x10(3) cm(-1). The latter value corresponds to the exclusive formation of the spin-excited Kr(+)((2)P(12)) ions, which may be used to obtain laser generation on the Kr(+)((2)P(12)-(2)P(32)) transition.     

Insertion of noble gas atoms into cyanoacetylene: an ab initio and matrix isolation study

A computational and experimental matrix isolation study of insertion of noble gas atoms into cyanoacetylene (HCCCN) is presented. Twelve novel noble gas insertion compounds are found to be kinetically stable at the MP2 level of theory, including four molecules with argon. The first group of the computationally studied molecules belongs to noble gas hydrides (HNgCCCN and HNgCCNC), and we found their stability for Ng = Ar, Kr, and Xe. The HNgCCCN compounds with Kr and Xe have similar stability to that of previously reported HKrCN and HXeCN. The HArCCCN molecule seems to have a weaker H-Ar bond than in the previously identified HArF molecule. The HNgCCNC molecules are less stable than the HNgCCCN isomers for all noble gas atoms. The second group of the computational insertion compounds, HCCNgCN and HCCNgNC, are of a different type, and they also are kinetically stable for Ng = Ar, Kr, and Xe. Our photolysis and annealing experiments with low-temperature cyanoacetylene/Ng (Ng = Ar, Kr, and Xe) matrixes evidence the formation of two noble gas hydrides for Ng = Kr and Xe, with the strongest IR absorption bands at 1492.1 and 1624.5 cm(-1), and two additional absorption modes for each species are found. The computational spectra of HKrCCCN and HXeCCCN fit most closely the experimental data, which is the basis for our assignment. The obtained species absorb at quite similar frequencies as the known HKrCN and HXeCN molecules, which is in agreement with the theoretical predictions. No strong candidates for an Ar compound are observed in the IR absorption spectra. As an important side product of this work, the data obtained in long-term decay of KrHKr+ cations suggest a tentative assignment for the CCCN radical.     

Fragmentation channels of K-shell excited rare-gas clusters studied by multiple-ion coincidence momentum imaging

Multiple-ion coincidence momentum imaging experiments were carried out for K-shell (1s) excited Ar clusters containing about 130 atoms and Kr clusters containing about 30, 90, and 160 atoms. The time-of-flight spectra reveal that the major products of the Coulomb explosion are singly charged ions. With increasing the number of charges generated in clusters, the momentum of monomer ions such as Ar(+) and Kr(+) increases, while that of cluster ions such as Ar(3) (+), Kr(2) (+), and Kr(3) (+) decreases. This observation indicates the site-specific decay process that the heavier ions appear in the central part of clusters. We have also investigated the momentum distribution in various fragmentation channels and the branching ratio of each channel at the Coulomb explosion. When the number N(coin) of coincidently detected ions is four, for example, the most frequent channel from Kr clusters containing 30 atoms is to emit simply four Kr(+) ions, but Kr(2) (+) ions participate in the fragmentation from the larger Kr clusters. The fragmentation channel in which two Ar(2) (+) ions are emitted becomes dominant with increasing N(coin), and the average momentum of Ar(2) (+) ion in this channel is larger than that in the channels where only single Ar(2) (+) is emitted.     

Hyperpolarized 83Kr and 129Xe NMR relaxation measurements of hydrated surfaces: implications for materials science and pulmonary diagnostics

In this proof of principle work, a technique is introduced to study hydrated surfaces using hyperpolarized (hp) 83Kr NMR spectroscopy. The longitudinal (T1) relaxation of hp-83Kr is shown to be extremely sensitive to the presence of adsorbed water on hydrophilic borosilicate and hydrophobic siliconized glass surfaces. The krypton surface relaxation is found to be largely independent of the total gas pressure applied to the studied materials, and the presented technique is therefore fairly robust. However, the relaxational properties of hp-83Kr can be "tuned" by adjusting the composition of the optical pumping gas mixture. This effect may be important for practical applications such as hp-83Kr MR imaging and can be achieved without sacrificing signal intensity. Complementary information to that of hp-83Kr surface relaxation data can be obtained from hp-129Xe relaxation measurements that are sensitive to the presence of paramagnetic surface sites. In contrast to the signal decay of hp-129Xe, the longitudinal relaxation of 83Kr is largely unaffected by paramagnetic impurities, and in some materials, 83Kr and 129Xe show comparable T1 times that are caused by two completely different relaxation mechanisms. Finally, the relaxation times of 83Kr in contact with bovine lung surfactant coated glass pores that are similar in size to mammalian alveoli are presented. The results suggest that in vivo MR studies may be feasible and could provide valuable information about changes in pulmonary surface chemistry.     

Formation of multi-charged Kr ions through photoionization of 2p electrons studied with a coincidence technique

Multi-charged Kr ions have been measured using monochromatized undulator radiation combined with a coincidence technique. The coincidence measurements between multi-charged ions and energy-selected Auger electrons have clarified decay processes, as follows. The Auger final states formed through L₃M₄₅M₄₅ decays turn significantly into Kr⁴⁺ and those through L₃M₂₃M₄₅ decays generate Kr⁵⁺ mainly. The Auger decays of L₃M₂₃M₂₃ types yield Kr⁶⁺ dominantly. These findings are consistent with the consideration on energy levels of Kr ions.     

RG+ formation following photolysis of NO-RG via the Ã-X transition: a velocity map imaging study

Kr(+) and Xe(+) formation following photodissociation of NO-RG (RG = Kr or Xe) molecules via the ?-X electronic transition in the 44,150-44,350 cm(-1) region has been investigated using velocity map imaging. Nuclear kinetic energy release (nKER) spectra indicate that the NO cofragment is produced in multiple vibrational states of the electronic ground state, with a high degree of rotational excitation. Photofragment angular distributions and nKERs are consistent with photo-induced charge transfer at the two-photon level followed by dissociative ionization at the three-photon level. RG(+) angular distributions showing highly parallel character relative to the laser polarization axis are indicative of a high degree of molecular alignment in the dissociating species.     

Rotational spectrum and internal dynamics of tetrahydrofuran-krypton

The rotational spectrum of the tetrahydrofuran-krypton van der Waals complex has been investigated by pulsed-jet Fourier transform microwave spectroscopy. The spectra of the (84)Kr and (86)Kr isotopologues have been assigned and the krypton atom is located nearly over the oxygen atom, almost perpendicular to the COC plane. Each rotational transition is split into two component lines due to, according to the observed Coriolis coupling term between the tunneling states, the residual pseudorotational effects of the ring in the complex. The splitting between the two vibrational sublevels is 87.462(2) and 87.062(2) MHz for the (84)Kr and (86)Kr isotopologues, respectively. These splittings have been used to determine the barrier to inversion, B(2) = 67 cm(-1). The dissociation energy has been estimated to be 3.7 kJ mol(-1) from centrifugal distortion effects.     

Kr和Kr2的实验和理论研究

利用超声分子束技术、同步辐射和反射式飞行时间质谱仪得到了Kr和Kr2的光电离质谱和光电离效率谱, 确定了Kr和Kr2的电离能. 利用Gaussian-03程序中的MP2(Full)/6-31G*, QCISD/cc-pVTZ以及B3LYP/6-31G方法优化了Kr2的结构, 计算了它们的振动频率和电离能, 计算结果显示: 当采用相同的理论水平和基组时, 随着Kr同位素质荷比(m/z)的增大, 它们结构和电离能保持不变, 而振动频率逐渐变小. 与此同时, 用G2方法计算了Kr (84)和Kr2 (168)的电离能, 它们的电离能的理论值与实验结果符合得比较好.