Henrik Kunttu

Vacuum rabi splitting and strong-coupling dynamics for surface-plasmon polaritons and rhodamine 6G molecules

We report on strong coupling between surface-plasmon polaritons (SPP) and Rhodamine 6G (R6G) molecules, with double vacuum Rabi splitting energies up to 230 and 110 meV. In addition, we demonstrate the emission of all three energy branches of the strongly coupled SPP-exciton hybrid system, revealing features of system dynamics that are not visible in conventional reflectometry. Finally, in analogy to tunable-Q microcavities, we show that the Rabi splitting can be controlled by adjusting the interaction time between waveguided SPPs and R6G deposited on top of the waveguide. The interaction time can be controlled with sub-fs precision by adjusting the length of the R6G area with standard lithography methods.

Photogeneration of ions via delocalized charge transfer states. I. Xe2H+ and Xe2D+ in solid Xe

Delocalized charge‐transfer excitations in solid xenon multiply doped with atomic halogens (I, Br, Cl) and hydrogen are demonstrated to lead to charge separation by trapping of the positive charge. As evidence of such a concept we present the first vibrational spectra of Xe2H+ and Xe2D+, which are believed to be vibrationally bound ions.

Photogeneration of ionic species in Ar, Kr and Xe matrices doped with HCl, HBr and HI

Abstract Photogeneration of Ar 2 H + , Kr 2 H + and Xe 2 H + and their deuterated counterparts is reported in H(D)Cl doped Ar, and H(D)X (X = Cl, Br or I) doped Kr and Xe matrices, respectively. The formation of these species is ascribed to optical access of the delocalized X/rare gas charge transfer states, and subsequent charge trapping processes. Once generated, the absorptions of the cations bleach thermally at low temperatures ( 12 K). The observed second-order decay kinetics is discussed in terms of charge-recombination involving a distribution of barrier heights. The deuterated cations bleach on a significantly longer time-scale. Bihalide ions, HX − 2 , of D ∞h symmetry are the other products formed in the photolysis. Annealing of the extensively irradiated HCl, HBr and HI doped xenon and HCl doped krypton yields strong infrared absorptions in the 1200–1600 cm −1 spectral region. These bands are tentatively ascribed to linear asymmetric (X-H—X) − ions perturbed by a nearby positive charge, or to (XeHX) + and (KrHX) + species.

Photodissociation of F2 and mobility of F atoms in crystalline argon

Experimental studies on the photodissociation of F2 in 12 K crystalline argon solids are reported, and compared with molecular dynamics (MD) simulations of the same system. At excess energies above 2.5 eV,the dissociation probability is near unity, in agreement with theory. At the longest experimentally accessible wavelength for photodissociation, 450 nm, which corresponds to a dissociation excess energy of 1.16 eV, the permanent dissociation probability is reduced to 0.05. This is an order of magnitude smaller than that predicted by the simulations. Possible sources for this discrepancy are discussed. Long range migration of F atoms, predicted by MD simulations, is demonstrated to occur both upon photodissociation of F2, and upon relaxation of argon fluorides. In the latter case, it is shown that with the initial impulse, the F atoms migrate on average a length of ∼70 A in the lattice. The thermal recombination of F atoms in both solid Ar and Kr are also characterized. The experimental studies are conduc...

Charge transfer and radiative dissociation dynamics in fluorine‐doped solid krypton and argon

The photodissociation of F2 in crystalline Kr is subject to only a minor cage effect—quantum yield of 0.5 at 308 nm, at T=12 K. Two‐photon‐induced harpooning in the same system leads to dissociation with near unit quantum efficiency; it is shown that this absorption is coherent with a giant cross section of 3(±2)×10−45 cm4  s at 275 nm. Excitation and emission spectra of charge‐transfer transitions in solid Kr doped with F atoms, and solid Ar multiply doped with F/Kr are reported. The vertical excitation in F/Kr leads to a state delocalized over immediate neighbors—assigned to Kr+6F−. This state localizes on a subpicosecond time scale to the triatomic Kr+2F− configuration. The latter relaxes radiatively (τr=140 ns), to the repulsive wall of the ground state (∼1 eV above ground). The excitation in F:Kr/Ar solids shows the diatomic KrF(B←X) resonances. From the analysis of the spectrum, a harmonic frequency ω=75(±3) cm−1 is extracted for F atoms in the ground state, consistent with molecular‐dynamics simula...

Thermal mobility of atomic hydrogen in solid argon and krypton matrices

Decay patterns of atomic hydrogen trapped in argon and krypton matrices are followed by electron paramagnetic resonance (EPR). Hydrogen atoms are generated by uv-photolysis of HBr and HCl precursor molecules. The EPR signals due to interstitially trapped hydrogen atoms in octahedral sites disappear near 16 and 24 K in Ar and Kr, respectively. Substitutionally trapped H atoms are thermally stable up to evaporation temperature of the solids. The fate of thermally released H atoms in Ar is exclusively due to geminate recombination of the parent molecule. The observed kinetics is well fitted with double exponential decay. The kinetic behavior reflects short-range dissociation and recombination dynamics in Ar. In the Kr matrix, a change from first-order to second-order kinetics is observed at higher concentrations as formation of molecular hydrogen becomes important. From bimolecular decay kinetics, a diffusion constant of 4×10−15 cm2 s−1 is deduced for H-atom diffusion in Kr at 26.9 K. The obtained activation...

Photogeneration of ions via delocalized charge transfer states. II. HX2− (X=Cl,Br,I) in rare gas matrices

Photolysis of HX (X=Cl,Br,I) doped rare gas matrices at excitation energies well below direct ionization of the solids is shown to yield efficient formation of hydrogen bihalide anions, HX2−. The formation dynamics of these ions is ascribed to a charge separation process initiated by optical access of the delocalized charge transfer states. The vibrational spectra of HX2− are presented and compared with previous work on M+⋅⋅⋅(HX2)− ion pairs, and the isoelectronic triatomic rare gas hydride cations.

On photochemistry of water in solid Xe: Thermal and light-induced decomposition of HXeOH and HXeH and formation of H2O2

A photochemical study of water (H2 16O, H2 18O, D2 16O, and D2 18O) in solid Xe is described. The water–Xe samples were irradiated at 193 nm and then annealed at 40–50 K, which led to formation of various isotopomers of Xe-containing molecules, HXeOH and HXeH. This diffusion-controlled formation of HXeH and HXeOH consumes the main part of hydrogen atoms generated in the matrix during photolysis. Both photodecomposition profiles and ultraviolet (UV) absorption spectra of HXeOH and HXeH feature a broad absorption band of these species around 240 nm corresponding to the transition to the repulsive excited states. It is also found that HXeOH and HXeH molecules can be thermally destroyed in similar time scales of ∼10 min at about 54 and 66 K, respectively. This clear difference between the decomposition temperatures for HXeOH and HXeH suggests the intrinsic basis of the decomposition process, which possibly occurs over the barriers of the bending coordinates. The absence of strong H–D isotope effect in this th...

Ab initio and molecular-dynamics studies on rare gas hydrides: Potential-energy curves, isotropic hyperfine properties, and matrix cage trapping of atomic hydrogen

Ground-state potential-energy curves and distance dependent isotropic hyperfine coupling (IHC) constants for ground-state H–RG (=Ne, Ar, Kr, Xe) are obtained at CCSD(T) (coupled-cluster single double triple) and MP4(SDQ) (fourth-order Moller–Plesset single double quadruple) levels, respectively, with an augmented basis set aug-Stuttgart (RG)/aug-cc-pVQZ (H). The obtained Rm and e are for NeH: 3.45 A and −1.36 meV; ArH: 3.65 A and −3.48 meV; KrH: 3.75 A and −4.32 meV; XeH: 3.90 A and −5.22 meV. The computed pair potentials are utilized in classical molecular-dynamics simulations of H–RG lattices. Along the classical trajectory, the many-body perturbation on the H atom hyperfine coupling constant is computed by pair-wise addition of the individual RG–H contributions obtained from the present quantum-chemical calculations. The computed IHC shifts are compared with electron paramagnetic resonance (EPR) spectra obtained in low-temperature matrix isolation experiments. For most cases this theoretical treatment ...

Infrared Induced Conformer Interconversion Processes in Low-Temperature Matrices

Molecules embedded in low-temperature matrices experience conformer interconversion processes due to IR- (or UV-)irradiation. This paper summarizes the known IR-induced conformational changes, of which the majority has been studied by using broad-band sources provided with filters. We focus at the thermal and IR-photochemical methods in obtaining information of conformational energetics of matrix isolated molecules, at the usefulness of ab initio calculations in assigning the spectra of conformers involved and in finding the reaction path on the ground state surface. The data obtained from a number of molecules is used to discuss possible mechanisms in both intramolecularly hydrogen-bonded and non-bonded molecules. Also possible indications of mode-selective phenomena in these processes are dealt with. In addition, common trends found for photorotamerization in different hosts are discussed.