0000000000114616
AUTHOR
Henrik Kunttu
Solvation of triplet Rydberg states of molecular hydrogen in superfluid helium
We report ab initio interaction potentials, transition dipole moments, and radiative lifetimes for the four lowest triplet states of ${\mathrm{H}}_{2}:$ $b$ ${}^{3}{\ensuremath{\Sigma}}_{u}^{+},$ $c$ ${}^{3}{\ensuremath{\Pi}}_{u},$ $a$ ${}^{3}{\ensuremath{\Sigma}}_{g}^{+},$ and $e$ ${}^{3}{\ensuremath{\Sigma}}_{u}^{+},$ and their response to the perturbation due to approaching ground state He atom. Hybrid density functional\char21{}quantum Monte Carlo calculations employing the ab initio interaction potentials are then used for calculating the liquid structure around the molecular excimers in bulk superfluid ${}^{4}\mathrm{He}.$ Calculations demonstrate a wide variety of possible solvation …
Relaxation Dynamics of Cr(acac)3 Probed by Ultrafast Infrared Spectroscopy
Ultrafast infrared spectroscopy is used to probe the dynamics of Cr(acac)3 upon ligand field (400 nm) and charge transfer state (345 nm) excitation. At both pump wavelengths, the ground state absorption bands are strongly bleached at zero delay, and new broad transient absorption bands appear red shifted from the bleached bands. Recovery of ground state bleach is dominated by a fast time constant (15 ps), while a small percentage recovers within 760−900 ps. Despite the extensive studies on Cr(acac)3 photophysics, the fast recovery of the ground state as a major channel is reported here for the first time. As a general result, the present communication emphasizes the great value of ultrafast…
Electronic Spectroscopy of C2 in Solid Rare Gas Matrixes
Electronic spectroscopy of the C(2) molecule is investigated in Ar, Kr, and Xe matrixes in the 150-500 nm range. In the Ar matrix, the D ((1)Sigma(u)(+)) <-- ((1)Sigma(g)(+)) Mulliken band near 240 nm is the sole absorption in the UV range, whereas in the Kr matrix additional bands in the 188-209 nm range are assigned to the Kr(n)()(+)C(2)(-) <-- Kr(n)()C(2) charge-transfer absorptions. Because of the formation of a bound C(2)Xe species, the spectral observations in the Xe matrix differ dramatically from the lighter rare gases: the Mulliken band is absent and new bands appear near 300 and 423 nm. The latter is assigned to the forbidden B'((1)Sigma(g)(+)) <-- X ((1)Sigma(g)(+)) transition, b…
EPR Studies of Atomic Impurities in Rare Gas Matrices
In this article we give an overview of the matrix isolation technique combined with electron paramagnetic resonance (EPR) detection for embedded atomic impurities in solid rare gases. A special emphasis is put on impurity – matrix coupling effects combining both experimental and theoretical approaches.
Collective optical resonances in networks of metallic carbon nanotubes
Abstract We demonstrate that thin films of randomly oriented metallic single-walled carbon nanotubes possess optical resonances with significant dispersion. The resonances are observed in the Kretschmann configuration as minima in reflection spectra close to 400 nm and 700 nm wavelengths. The dispersions are visible only when the material is excited with s -polarized light, and most prominent in layers with thickness near 100 nm. We conclude that magnetic plasmon polaritons arising from intertube interactions are a likely explanation. Closeness of the M 11 and M 22 transition energies to the observed resonances points to a possible coupling with excitons.
Electronic Absorption Spectra of HXeCl, HXeBr, HXeI, and HXeCN in Xe Matrix
The electronic UV absorption spectra of thermal reaction products H−Xe−Y (Y= Cl, Br, I, or CN) have been measured in solid Xe at 12 K. The spectra are obtained after the annealing of an extensively...
Surface plasmon effects on carbon nanotube field effect transistors
Herein, we experimentally demonstrate surface plasmon polariton (SPP) induced changes in the conductivity of a carbon nanotube field effect transistor (CNT FET). SPP excitation is done via Kretschmann configuration while the measured CNT FET is situated on the opposite side of the metal layer away from the laser, but within reach of the launched SPPs. We observe a shift of 0.4 V in effective gate voltage. SPP-intermediated desorption of physisorbed oxygen from the device is discussed as a likely explanation of the observed effect. This effect is visible even at low SPP intensities and within a near-infrared range. peerReviewed
Vibrational relaxation of matrix-isolated carboxylic acid dimers and monomers.
Femtosecond mid-IR transient absorption spectroscopy was used to probe the vibrational dynamics of formic acid and acetic acid isolated in solid argon following excitation of the fundamental transition of the carbonyl stretching mode. Carboxylic acids form extremely stable H-bonded dimers, hindering the study of the monomeric species at equilibrium conditions. The low-temperature rare-gas matrix isolation technique allows for a unique control over aggregation enabling the study of the monomer vibrational dynamics, as well as the dynamics of two distinct dimer structures (cyclic and open chain). This study provides insight into the role of the methyl rotor and hydrogen bonding in the vibrati…
Charge transfer states of C2 in Kr clusters
Abstract Ab initio and diatomics-in-ionic-systems (DIIS) calculations are carried out for the C 2 –Kr pair and C 2 –Kr n clusters, respectively. Energetics and transition dipole moments between the ground and excited states are obtained from the calculations. This data is then used to predict the UV charge transfer absorption spectrum of C 2 embedded in Kr n clusters with n = 1, 12, and 224. The results reveal discrete structure in the computed UV spectrum, which is mainly related to the spin–orbit splitting of Kr + .
Temperature Dependence of Electronic Transitions of Single-Wall Carbon Nanotubes: Observation of an Abrupt Blueshift in Near-Infrared Absorption
Near-infrared (NIR) absorption spectra of single-wall carbon nanotube (SWNT) films are studied between 10 and 293 K. The most prominent effect is the shift of bands with temperature. Some nanotubes show a redshift of transition upon increasing temperature while some show blueshift and others show no shift. The shift is interpreted to originate mainly from the effect of strain induced in the tubes because of interaction with the environment. In particular, at temperatures T = 175−225 K, for some bands, there is an abrupt large blueshift, which is interpreted to originate from interaction of the nanotubes with water. Two models could be considered to explain the effect: (1) strain induced by…
Molecular coupling of light with plasmonic waveguides.
We use molecules to couple light into and out of microscale plasmonic waveguides. Energy transfer, mediated by surface plasmons, from donor molecules to acceptor molecules over ten micrometer distances is demonstrated. Also surface plasmon coupled emission from the donor molecules is observed at similar distances away from the excitation spot. The lithographic fabrication method we use for positioning the dye molecules allows scaling to nanometer dimensions. The use of molecules as couplers between far-field and near-field light offers the advantages that no special excitation geometry is needed, any light source can be used to excite plasmons and the excitation can be localized below the d…
Rotation of methyl radicals in molecular solids.
Electron spin resonance (ESR) measurements were carried out to study the rotation of methyl radicals (CH(3)) in solid carbon monoxide, carbon dioxide, and nitrogen matrices. The radicals were produced by dissociating methane by plasma bursts generated by a focused 193 nm ArF excimer laser radiation during the gas condensation on the substrate. The ESR spectra exhibit anisotropic features that persist over the temperature range examined, and in most cases this indicates a restriction of rotation about the C(2) symmetry axis. A nonrotating CH(3) was also observed in a CO(2) matrix. The intensity ratio between the symmetric (A) and antisymmetric (E) nuclear spin states was recorded as a functi…
Photodissociation of Formaldehyde in Rare Gas (Xe, Kr, Ar, and Ne) Matrixes
Infrared (IR) spectroscopy and electron paramagnetic resonance (EPR) are combined to study photodissociation of formaldehyde at photolysis wavelengths 308, 248, and 193 nm in rare gas matrixes. The...
Vacuum Rabi splitting for surface plasmon polaritons and Rhodamine 6G molecules
We report on strong coupling between surface-plasmon polaritons and Rhodamine 6G molecules at room temperature. As a reference to compare with, we first determine the dispersion curve of (uncoupled) surface plasmon polaritons on a 50 nm thick film of silver. Consequently, we determine the dispersion curve of surface plasmon polaritons strongly coupled to Rhodamine 6G molecules, which exhibits vacuum Rabi splitting. Depending on the Rhodamine 6G concentration, we find splitting energies between 0.05 eV and 0.13 eV.
Role of Vibrational Dynamics in Electronic Relaxation of Cr(acac)3
Ultrafast energy relaxation of Cr(acac)3 dissolved in tetrachloroethylene (TCE) is studied by time-resolved infrared (TRIR) spectroscopy by using electronic and vibrational excitation. After electronic excitation at 400 or 345 nm, the ground state recovers in two time scales: 15 ps (major pathway) and 800 ps (minor pathway), corresponding to fast electronic transition to the ground state and intermediate trapping on the long-lived (2)E state followed by intersystem crossing (ISC) to the ground state. The quantum yield for the fast recovery of the ground state depends on the excitation wavelength, being higher for 345 nm. Vibrational cooling (VC) occurs on the electronic excited states with …
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 pre…
Rotation of methyl radicals in a solid krypton matrix
Electron spin resonance (ESR) measurements were carried out to study the rotation of methyl radicals (CH(3)) in a solid krypton matrix at 17-31 K temperature range. The radicals were produced by dissociating methane by plasma bursts generated by a focused 193 nm excimer laser radiation during the krypton gas condensation on the substrate. The ESR spectrum exhibits only isotropic features at the temperature range examined, and the intensity ratio between the symmetric (A) and antisymmetric (E) spin state lines exhibits weaker temperature dependence than in a solid argon matrix. However, the general appearance of the methyl radical spectrum depends strongly on temperature due to the pronounce…
Trapping of laser-vaporized alkali metal atoms in rare-gas matrices
Abstract Alkali metal atoms prepared by laser ablation of solid Li and Na are trapped in Ar, Kr, and Xe matrices and studied by electron paramagnetic resonance spectroscopy (EPR) at 15 K. Evidence for tight trapping sites, not observed for atoms generated by conventional Knudsen oven techniques, is presented. The novel tight trapping sites are characterized by a large increase in the isotropic hyperfine coupling constant and a simultaneous decrease in the isotropic g -value. Based on the EPR data, it is suggested that the observed tight trapping corresponds to single substitution of lattice atoms in Ar, Kr, and Xe matrices.
Frequency conversion of propagating surface plasmon polaritons by organic molecules
We demonstrate frequency conversion of surface plasmon polaritons (SPP) by utilizing the coupling between organic dye molecules and SPP. Launching of SPPs into a plasmonic waveguide is done in two ways: by optically excited molecules and by quantum dots (QDs). QDs are demonstrated to overcome the major problem of bleaching occurring with molecules. The SPP propagates tens of micrometers and clear frequency conversion is observed in the SPP spectrum after passing an area of converter molecules. The use of molecules and QDs as elements of all-plasmonic devices has the potential for high integration and use of self-assembly in fabrication. Peer reviewed
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 lith…
Structure and Matrix Isolation Infrared Spectrum of Formyl Fluoride Dimer: Blue-Shift of the C−H Stretching Frequency
Infrared spectroscopy (IR) of formyl fluoride (HCOF) dimer is studied in low-temperature argon and krypton matrixes. New IR absorptions, ca. 17 cm(-1) blue shifted from the monomer C-H stretching fundamental, are assigned to the HCOF dimer. The MP2/6-311++G calculations were utilized to define structures and harmonic frequencies of various HCOF dimers. Among the four optimized structures, the dimer having two C-H...O hydrogen bonds possesses strongest intermolecular bonding. The calculated harmonic frequencies of this dimer structure are shifted from the monomer similarly as observed in the experiment. Thus, we suggest that the experimentally observed blue shifted C-H bands belong to the di…
Ultrafast Electronic and Vibrational Energy Relaxation of Fe(acetylacetonate)3 in Solution
Transient mid-infrared spectroscopy is used to probe the dynamics initiated by excitation of ligand-to-metal (400 nm) and metal-to-ligand (345 nm) charge transfer states of FeIII complexed with acetylacetonate (Fe(acac)3, where acac stands for deprotonated anion of acetylacetone) in solution. Transient spectra in the 1500-1600 cm-1 range show two broad absorptions red-shifted from the bleach of the nu(CO) (approximately 1575 cm-1) and nu(C=C) (approximately 1525 cm-1) ground state absorptions. Bleach recovery kinetics has a time constant of 12-19 ps in chloroform and tetrachloroethylene and it decreases by 30-40% in a 10% mixture of methanol in tetrachloroethylene. The transient absorptions…