Three-photon resonance enhanced excitation spectrum of atomic thallium

We present first measurements on the resonance enhanced three-photon excitation in thallium, using a Nd:YAG laser pumped dye laser in conjunction with a thermionic diode ion detector. The even-parity 6s²ns²S_1/2 (15 ? n ? 31) and nd ²D_5/2 (13 ? n ? 42) Rydberg states have been observed. The measured level energies reveal a dynamic shift from the photoabsorption values, which is decreasing with increasing n, while the asymmetry in the line profile is observed to be increasing with increasing n. In addition, an autoionising level (sp²⁴P_3/2) adjacent to the ionization threshold has been observed and quantitatively analyzed using the Fano’s photoionization cross-section relation for an isolated autoionising resonance.     

Resonantly enhanced three-photon excitation spectra of lithium

We present the first measurement on the resonantly enhanced three-photon excitation spectra of natural lithium using a Nd:YAG laser pumped dye laser in conjunction with a thermionic diode ion detector. Exploiting the linear and circular polarizations, the np ²P_3/2(8 ? n ? 11) and nf  ²F_7/2 (8 ? n ? 38) series have been observed via three-photon excitation from the ground state. The measured level energies reveal a dynamic shift from calculated values, which increases with an increase of the principal quantum number n. The ac stark shift and line broadening mechanisms are studied as a function of laser intensity. It is noted that the width increases and the line center shifts towards the higher energy side as the laser intensity is increased. The maximum observed shift for the 12f ²F_7/2 line is 0.33 cm⁻¹ corresponding to the laser intensity variation from 1.34 × 10¹² W/m² to 1.03 × 10¹³ W/m², whereas its width increases from 0.36 cm⁻¹ to 0.82 cm⁻¹.     

Investigation of the D Π state of NaK by polarisation labelling spectroscopy

Two-colour polarisation labelling experiments measuring the D-X system of NaK have furnished observations of the D ¹Π state of NaK up to v″ = 42. The last observed level is located 7 cm⁻¹ below the Na(3p ²P_3/2) + K(4s) atomic asymptote, 22247.15 cm⁻¹ above the minimum of the electronic ground state, clearly indicating the dissociation products of this state. The vibrational progressions all exhibit irregular intervals, predominantly because of strong interactions with the nearby d ³Π state, which also dissociates to Na(3p) + K(4s) atoms. The polarisation data have been combined with some resolved fluorescence D-X transitions, and analysed by fitting to spectroscopic parameters and to an analytical potential curve. A full deperturbation treatment has not been attempted, but a ‘robust’ weighting scheme has been used to reduce the influence of levels that cannot be properly represented by a single channel model. Parameters determined in a fit to a potential curve include T_e = 20090.18 ± 0.02 cm⁻¹, well depth 2157.0 ± 0.3 cm⁻¹, R_e = 4.1547 ± 0.0002 Å, with an unweighted root mean square error of 0.12 cm⁻¹ for 959 data.     

Fast relaxation of the metastable helium state 2S0 in collisions with molecules and collisional lasing on the He (2P1-2S0) transition

In the present study, the laser absorption method was used to measure the rates of quenching of the metastable state He(2¹S₀), the lower laser level in the self-terminating helium laser, with H₂O, NH₃, N₂O, and CO₂ molecules. For the above molecules, the quenching rate constants were found to equal (1.2 ± 0.3)10^− 9, (0.8 ± 0.2)10^− 9, (1.9 ± 0.2)10^− 9 and (2.2 ± 0.4)10^− 9 cm³ s^− 1. Under excitation with long (up to 750 ns) open discharge generated electron beam pulses, lasing on the transition He (2¹P₁⁰-2¹S₀) was examined. In the mixtures He-H₂O and He-NH₃, lasing durations almost equal to the pump-pulse duration were obtained. In the mixtures of He with CO₂ and N₂O, no lasing prolonged in comparison with pure helium was found. The data obtained were explained considering two quenching mechanisms for the state He(2¹S₀): in collisions with molecules and in collisions with plasma electrons having low energies due to fast relaxation of the vibrational states of H₂O and NH₃ molecules.     

Resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of the selected rotamers of m-methoxyaniline and o-methoxyaniline

We report the resonant two-photon ionization and mass-analyzed threshold ionization (MATI) spectra of m-methoxyaniline and o-methoxyaniline. The vibronic features of m-methoxyaniline are built on 34308 ± 2 and 34495 ± 2 cm⁻¹ corresponding to the origins of the S₁ ← S₀ electronic transition (E₁’s) of the cis and trans rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 59983 ± 5 and 60879 ± 5 cm⁻¹ for these two species. o-Methoxyaniline is found to have only one stable structure whose E₁ and IE are 33875 ± 2 and 58678 ± 5 cm⁻¹, respectively. Most of the active vibrations of m- and o-methoxyaniline in the electronically excited S₁ and cationic ground D₀ states result from the in-plane ring vibrations. Comparing these data with those of p-methoxyaniline allows us to learn about the vicinal substitution effects resulting from the relative locations of the NH₂ and OCH₃ substituents.     

Galvanomagnetic properties of air-stable and highly conductive potassium-intercalated graphite sheet

Magnetoresistance and Hall coefficient of air-stable potassium-intercalated graphite sheets (hereafter abbreviated as K-PGS) were determined at room temperature. The magnitude of the magnetoresistance and the absolute value of Hall coefficient of K-PGS decreased with increasing potassium content of K-PGS, n_K/n_C. Two-carrier model was used for calculating carrier density and mobility. The electron density increased with increasing n_K/n_C: 3.07×10²⁰ cm⁻³ (n_K/n_C=0.005), 5.67×10²⁰ cm⁻³ (n_K/n_C=0.008) and 6.40×10²⁰ cm⁻³ (n_K/n_C=0.011). The value of the electron density of K-PGS with n_K/n_C=0.011 (nominal composition KC₉₁) was about 80% of the reported value, 7.8×10²⁰ cm⁻³, for KC₄₈ (n_K/n_C=0.021) prepared from HOPG (highly oriented pyrolytic graphite). The mobility decreased with increasing n_K/n_C: 2.11×10³ cm² V⁻¹ s⁻¹ (n_K/n_C=0.005), 1.42×10³ cm² V⁻¹ s⁻¹ (n_K/n_C=0.008) and 1.34×10³ cm² V⁻¹ s⁻¹ (n_K/n_C=0.011). The value of the mobility of K-PGS with n_K/n_C=0.011 was about 60% of the reported value (2300 cm² V⁻¹ s⁻¹) for KC₄₈ prepared from HOPG.     

Two-color three-photon excitation studies of thallium Rydberg states

We present new data on the even-parity Rydberg states of atomic thallium using two-step three-photon laser excitation technique in conjunction with a thermionic diode ion detector. Atoms are excited from the 6p ²P_1/2 ground state to the 7p ²P_1/2 intermediate state via two-photon excitation and subsequently promoted to the high lying ns ² S_1/2 and nd ²D_3/2 Rydberg states. The first ionization potential of thallium is determined as 49,266.66(1) cm^-1 using data for the ns ² S_1/2 (25 ≤ n ≤ 54) and nd ²D_3/2 (24 ≤ n ≤ 65) Rydberg series. This value is believed to be more accurate because the contribution due to the hyperfine structure splitting of the 7p ²P_1/2 state (0.07185 cm^-1) is much smaller as compared to that of the 6p ²P_1/2 ground state (0.711 cm^-1).     

Single crystal EPR and optical absorption study of Cr doped l-histidine hydrochloride monohydrate

EPR study of the Cr³⁺ ion doped l-histidine hydrochloride monohydrate single crystal is done at room temperature. Two magnetically inequivalent interstitial sites are observed. The hyperfine structure for Cr⁵³ isotope is also obtained. The zero field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations and the parameters are: D=(300±2)×10⁻⁴ cm⁻¹, E=(96±2)×10⁻⁴ cm⁻¹, g_x=1.9108±0.0002, g_y=1.9791±0.0002, g_z=2.0389±0.0002, A_x=(252±2)×10⁻⁴ cm⁻¹, A_y=(254±2)×10⁻⁴ cm⁻¹, A_z=(304±2)×10⁻⁴ cm⁻¹ for site I and D=(300±2)×10⁻⁴ cm⁻¹, E=(96±2)×10⁻⁴ cm⁻¹, g_x=1.8543±0.0002, g_y=1.9897±0.0002, g_z=2.0793±0.0002, A_x=(251±2)×10⁻⁴ cm⁻¹, A_y=(257±2)×10⁻⁴ cm⁻¹, A_z=(309±2)×10⁻⁴ cm⁻¹ for site II, respectively. The optical absorption studies of single crystals are also carried out at room temperature in the wavelength range 195-925 nm. Using EPR and optical data, different bonding parameters are calculated and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are: B=636, C=3123, Dq=2039 cm⁻¹, h=1.46 and k=0.21, respectively.     

Kinetic studies of chlorobenzene reactions with hydrogen atoms and phenyl radicals and the thermochemistry of 1-chlorocyclohexadienyl radicals

Atomic H and Cl were monitored by time-resolved resonance spectroscopy in the vacuum ultraviolet, following 193 nm laser flash photolysis of C₆H₅Cl and mixtures with NH₃, over 300-1020 K and with Ar bath gas pressures from 30 to 440 mbar. Below 550 K simple exponential decays of [H] were observed, and attributed to addition to form chlorocyclohexadienyl radicals. This addition was reversible over 550-630 K and the equilibrium constant was determined by a third law approach. The addition rate constant can be summarized as (1.51 ± 0.11) × 10⁻¹¹exp((−1397 ± 29)/T) cm³ molecule⁻¹ s⁻¹ (300-630 K, 1σ uncertainties), and the C-H bond dissociation enthalpy in 1-chlorocyclohexadienyl was determined to be 108.1 ± 3.3 kJ mol⁻¹ at 298 K. At higher temperatures the photolysis of chlorobenzene yielded H atoms, which is attributed to the reaction of phenyl with chlorobenzene with a rate constant of (4.5 ± 1.8) × 10⁻¹⁰exp((−4694 ± 355)/T) cm³  molecule⁻¹ s⁻¹ over 810-1020 K. These and other reaction pathways are discussed in terms of information about the potential energy surface obtained via B3LYP/6-311G(2d,d,p) density functional theory.     

Rate coefficients measurement for the energy-pooling collisions Cs(5D) + Cs(5D) → Cs(6S) + Cs(nl = 9D, 11S, 7F)

We report experimental rate coefficients for the energy-pooling collisions Cs(5D) + Cs(5D) → Cs(6S) + Cs(nl = 9D, 11S, 7F). In the experiment the Cs(5D) state was populated via photodissociation of Cs₂ molecules using an argon-ion laser at wavelength 488.0 nm. We also consider the competing process 6P_1/2 + 7S → 6S + (nl = 9D, 11S, 7F) that might also populate 9D, 11S and 7F. An intermodulation technique was used to select the fluorescence contributions due only to the process 6P_1/2 + 7S → 6S + (nl = 9D, 11S, 7F). The excited atom (nl_J) density and spatial distribution were mapped by monitoring the absorption of a counterpropagating probe laser beam tuned to various transitions. The measured excited atom densities are combined with measured fluorescence ratios to yield rate coefficients for the energy-pooling collisions Cs(5D) + Cs(5D) → Cs(6S) + Cs(nl = 9D, 11S, 7F). The rate coefficients for nl = 9D, 11S, 7F are (4.1 ± 2.0) × 10⁻¹⁰ cm³ s⁻¹, (1.6 ± 0.8) × 10⁻¹⁰ cm³ s⁻¹ and (3.6 ± 1.8) × 10⁻¹⁰ cm³ s⁻¹, respectively. The contributions to the rate coefficients from other energy transfer processes are also discussed.     

EPR and optical absorption study of Cr-doped ammonium oxalate monohydrate single crystals

The electron paramagnetic resonance (EPR) study of the Cr³⁺-doped ammonium oxalate monohydrate (AOM) single crystal is done at room temperature. Two magnetically inequivalent sites for chromium are observed. The hyperfine structure for Cr⁵³ isotope is also obtained. The spin Hamiltonian parameters are evaluated as: D=(309±2)×10⁻⁴ cm⁻¹, E=(103±2)×10⁻⁴ cm⁻¹, g=1.9820±0.0002, A=(161±2)×10⁻⁴ cm⁻¹ for site I and D=(309±2)×10⁻⁴ cm⁻¹, E=(103±2)×10⁻⁴ cm⁻¹, g=1.9791±0.0002, A=(160±2)×10⁻⁴ cm⁻¹ for site II, respectively. On the basis of EPR data the site symmetry of Cr³⁺ doped single crystal is discussed. The optical absorption spectra are recorded in 195-925 nm wavelength range at room temperature. The energy values of different orbital levels are determined. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The values of different parameters are B=803, C=3531, D_q=2208 cm⁻¹, h=0.59 and k=0.21, where B and C are Racah parameters, D_q is crystal field parameter and h and k are nephelauxetic parameters, respectively.     

Variable-temperature FT-IR studies on the thermodynamics of carbon dioxide adsorption on a faujasite-type H-Y zeolite

Adsorption of carbon dioxide on a faujasite-type H-Y zeolite (Si:Al = 2.6:1) was studied by variable-temperature (200-290 K range) infrared spectroscopy. Adsorbed CO₂ molecules interact with the Brønsted acid Si(OH)Al groups located inside the zeolite supercage, bringing about a characteristic bathochromic shift of the O-H stretching mode from 3645 cm⁻¹ (free OH group) to 3540 cm⁻¹ (hydrogen-bonded CO₂ adsorption complex). Simultaneously, the asymmetric (ν₃) mode of adsorbed CO₂ is observed at 2353 cm⁻¹. From the observed variation of the integrated intensity of the 3645 and 2353 cm⁻¹ IR absorption bands upon changing temperature, corresponding values of standard adsorption enthalpy and entropy were found to be ΔH° = −28.5(±1) kJ mol⁻¹ and ΔS° = −129(±10) J mol⁻¹ K⁻¹. Comparison with the reported values of ΔH° for CO₂ adsorption on other zeolites is briefly discussed.     

Nonlinear optical properties of CNHP4 nanofibers: Molecular dipole orientations and two photon absorption cross-sections

Polarized second harmonic measurements are used to determine the in- and out-of plane orientations of molecular dipoles in optical active, elongated, surface bound nanoaggregates. As a specific example, nonlinear optical active nanofibers grown from CNHP4 molecular dipoles on muscovite mica are investigated. The orientation of the dipoles relative to the substrate is found to be 7 ± 5°, whereas that of the dipoles relative to the long nanofiber axes is ± 13 ± 5°. Following 780 nm femtosecond laser excitation, the two photon action potential ησ₂ for CNHP4 is determined to be 4.7 × 10⁻⁵⁴ cm⁴ s/photon. For comparison, ησ₂ for para-hexaphenylene nanofibers is measured to be 12 × 10⁻⁵⁴ cm⁴ s/photon.     

Influence of ordering change on the optical and thermal properties of inflation polyethylene films

Changes of thermal diffusivity inside femtosecond laser-structured volumes as small as few percent were reliably determined (with standard deviation less than 1%) with miniaturized sensors. An increase of thermal diffusivity of a crystalline high-density polyethylene (HDPE) inflation films by 10-20% from the measured (1.16 ± 0.01) × 10⁻⁷ m² s⁻¹ value in regions not structured by femtosecond laser pulses is considerably larger than that of non-crystalline polymers, 0-3%. The origin of the change of thermal diffusivity are interplay between the laser induced disordering, voids’ formation, compaction, and changes in molecular orientation. It is shown that laser structuring can be used to modify thermal and optical properties. The birefringence and infrared spectroscopy with thermal imaging of CH₂ vibrations are confirming inter-relation between structural, optical, and thermal properties of the laser-structured crystalline HDPE inflation films. Birefringence modulation as high as Δn ∼ ± 1 × 10⁻³ is achieved with grating structures.     

Torsion-rotation global analysis and database for the CH3OH isotopomer of methanol

Fourier-transform far-infrared spectra of CH₃¹⁸OH in the 15-470 cm⁻¹ region have been analyzed by means of the Ritz assignment program. The far-infrared data have been combined with the literature microwave and millimeter-wave measurements in a full global fitting of the first three torsional states (ν_t = 0, 1, and 2) of the CH₃¹⁸OH ground vibrational state. The fitted dataset includes 550 microwave and millimeter-wave lines and more than 17 000 Fourier-transform transitions covering the quantum number ranges J ? 30, K ? 15, and ν_t ? 2. With incorporation of 79 adjustable parameters, the global fit achieved convergence with an overall weighted standard deviation of 1.072, essentially to within the assigned measurement uncertainties of ±50 kHz for almost all of the microwave and millimeter-wave lines and ±6 MHz (0.0002 cm⁻¹) to ±15 MHz (0.0005 cm⁻¹) for the Fourier-transform far-infrared measurements. Based on the global fit results, a database has been compiled containing transition frequencies, quantum numbers, lower state energies and transition strengths. This database will provide support for present and future astronomical studies, such as the on-going Orion surveys in preparation for the launch of the Herschel Space Observatory, in identifying isotopic methanol contributions to interstellar spectra.     

Lifetime measurements in the triplet system of Mg I

In an atomic beam the metastable 3s3p ³ P-states of Mg I were populated by electron impact. A pulsed tunable dye laser was used to excite the metastable atoms to the 3snd³ D-(n=3–7) and to the 3sns³ S ₁-states (n=4and 6). Observing the time dependence of the reemitted resonance light the lifetimes of these states were measured.     

Interatomic potentials for the ground state X 0 and the two excited states 1, 0 of the intercombination cadmium line 326.1 nm broadened by Kr pressure

The temperature dependence of the Cd line absorption profile at 326.1 nm perturbed by Kr has been carefully studied over a spectral range extending from 800 cm⁻¹ in the blue wing to 1200 cm⁻¹ in the red wing using a high-resolution double-beam spectrometer. The atomic densities of krypton (N_Kr) and cadmium (N_Cd) were (2.015±0.07)×10¹⁹ and (3.62±0.05)×10¹⁸ cm⁻³, respectively. The temperature dependence of the studied line profile was analyzed in the framework of the quasi-static theory. The van der Waals coefficient differences between the ground ¹0⁺ state and the two excited states ³0⁺ and ³1 (ΔC₆⁰ and ΔC₆¹) were obtained from the near red wing profile using Kuhn's law. The values of ΔC₆⁰ and ΔC₆¹ are found to be equal to 37.8±2 and 58.5±3 eV Å⁶, respectively. The ground (X ¹0⁺), and the excited (³1, ³0⁺) state potentials at the internuclear separations from 3.2 to 6.3 Å were determined. The well depths with their positions for these states are respectively equal to 134±7 cm⁻¹, 3.95±0.2 Å; 72.3±4 cm⁻¹, 4.95±0.3 Å; and 471±12 cm⁻¹, 3.6 Å. The obtained well depths with their allowable errors are in good agreement with the values obtained before for the Cd-Kr system from some theoretical results and molecular beams experiments.     

Velocity changing collisions in the laser saturation spectra of Rb D2 F″ = 2

The saturation absorption technique is applied to the ⁸⁷Rb ²S_1/2 F″ = 2 → ²P_3/2 F′ = 1, 2 and 3 transitions to study the effect of velocity changing collisions (VCC). The VCC caused Doppler pedestal increases with argon pressure from 0 to 110 mTorr and decreases with modulation frequencies of 700-3200 Hz. The resonances of the velocity selective, saturated optical pumping are washed out for pressure of 110 mTorr. The magnitude of the Doppler pedestal relative to the homogeneous features, yields a rate for velocity changing collisions of 6.5 ± 0.2 × 10⁻¹⁰ cm³ s⁻¹.     

Vibronic and cation spectroscopy of m-chloroaniline

We applied the resonant two-photon ionization and mass-analyzed threshold ionization spectroscopic techniques to record the vibronic and cation spectra of m-chloroaniline. The band origin of the first electronic transition was found to be 33 658 ± 2 cm⁻¹, whereas the adiabatic ionization energy was determined to be 63 958 ± 5 cm⁻¹. Within our experimental detection limit, these measured values are the same for both of the ³⁵Cl and ³⁷Cl isotopomers. The observed active modes of this molecule in the electronically excited S₁ and cationic ground D₀ states mainly involve the in-plane ring deformation and substituent-sensitive bending vibrations.     

Illumination dependence of I-V and C-V characterization of Au/InSb/InP(1 0 0) Schottky structure

The effects of surface preparation and illumination on electric parameters of Au/InSb/InP(100) Schottky diode were investigated, in the later diode InSb forms a fine restructuration layer allowing to block In atoms migration to surface. In order to study the electric characteristics under illumination, we make use of an He-Ne laser of 1 mW power and 632.8 nm wavelength. The current-voltage I(V_G), the capacitance-voltage C(V_G) measurements were plotted and analysed. The saturation current I_s, the serial resistance R_s and the mean ideality factor n are, respectively, equal to 2.03 × 10⁻⁵ A, 85 Ω, 1.7 under dark and to 3.97 × 10⁻⁵ A, 67 Ω, 1.59 under illumination. The analysis of I(V_G) and C(V_G) characteristics allows us to determine the mean interfacial state density N_ss and the transmission coefficient θ_n equal, respectively, to 4.33 × 10¹² eV⁻¹ cm⁻², 4.08 × 10⁻³ under dark and 3.79 × 10¹² eV⁻¹ cm⁻² and 5.65 × 10⁻³ under illumination. The deep discrete donor levels presence in the semiconductor bulk under dark and under illumination are responsible for the non-linearity of the C⁻²(V_G) characteristic.