The Phosphorescence Excitation Spectrum of Jet-Cooled Xanthione in the Region of the T1←S0 and S1←S0 Absorption Transitions

The ³A₂(nπ*)→¹A₁X (T₁→S₀) phosphorescence excitation spectrum of jet-cooled xanthione was investigated in the region 14 920-17 600 cm⁻¹. The structure observed is shown to be due to the T₁←S₀ absorption and an assignment in terms of the vibronic structure of that band is proposed. A previous assignment of the S₁←S₀ origin is considered in detail and the transition involved is shown to be most probably due to absorption of a vibronic triplet state T_1z,ν7. An alternative but tentative assignment of the S_1,0←S_0,0 transition is suggested. Comparison is made with previous spectroscopic and theoretical work on the molecule and its congeners, 4H-pyran-4-thione and 4H-1-benzopyran-4-thione.     

Synthesis and nonlinear optical characterization of SnO2 quantum dots

The present paper demonstrates the preparation and characterization of SnO₂ semiconductor quantum dots. Extremely small ∼1.1 and ∼1.4 nm SnO₂ samples were prepared by microwave assisted technique with a frequency of 2450 MHz. Based on XRD analysis, the phase, crystal structure and purity of the SnO₂ samples are determined. UV-vis measurements showed that, for the both size of SnO₂ samples, excitonic peaks are obtained at ∼238 and ∼245 nm corresponding to ∼1.1 nm (sample 1) and ∼1.4 nm (sample 2) sizes, respectively. STM analysis showed that, the quantum dots are spherical shaped and highly monodispersed. At first, the linear absorption coefficients for two different sizes of SnO₂ quantum dots were measured by employing a CW He-Ne laser at 632.8 nm and were obtained about 1.385 and 4.175 cm⁻¹, respectively. Furthermore, the nonlinear refractive index, n₂, and nonlinear absorption coefficient, β, were measured using close and open aperture Z-scan respectively using the same laser. As quantum dots have strong absorption coefficient to obtain purely effective n₂, we divided the closed aperture transmittance by the corresponding open aperture in the same incident beam intensity. The nonlinear refraction indices of these quantum dots were measured in order of 10⁻⁷ (cm²/W) with negative sign and the nonlinear absorption coefficients were obtained for both in order of 10⁻³ (cm/W) with positive sign.     

Electronic energy levels of lithium gadolinium tetraphosphate (LiGdP4O12)

The positions of 15 electronic energy levels above the ground level ⁸S_7/2 of Gd³⁺ in flux-grown single crystals of LiGdP₄O₁₂ have been determined from 4f–4f transitions observed in absorption spectra in the range 190–340 nm at T = 293 K. The experimental energy levels have been compared with theoretical ones obtained by two parameters, F₂ = 392 cm⁻¹ and ζ_4f = 1525 cm⁻¹, in the intermediate coupling approximation.     

Line strengths of CO2: 4550-7000 cm

Line positions and strengths of ¹²C¹⁶O₂ were measured between 4550 and 7000 cm⁻¹ using near infrared absorption spectra recorded at 0.01-0.013 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory at Kitt Peak, Arizona. These were retrieved from 42 laboratory spectra obtained at room temperature with five absorption cells having various optical path lengths (from 0.1 to 409 m) filled with natural and enriched samples of CO₂ at pressures ranging from 2 to 581 Torr. In all, band strengths and Herman-Wallis-like F-factor coefficients were determined for 58 vibration-rotation bands from the least-squares fits of over 2100 unblended line strengths; strengths of 34 of these bands had not been previously reported. Band strengths in natural abundance generally ranged from 3.30 × 10⁻²⁰ to 2.8 × 10⁻²⁵ cm⁻¹/molecule cm⁻² at 296 K. It was found that the high J transitions (J′ ? 61) of the 20012 ← 00001 band centered at 4977.8347 cm⁻¹ are perturbed, affecting both measured positions and strengths. Two other interacting bands, 21113e ← 01101e and 40002e ← 01101e, were also analyzed using degenerate perturbation theory. Comparisons with corresponding values from the literature indicate that absolute accuracies better than 1% and precisions of 0.5% were achieved for the strongest bands.     

Optical gain due to the Eu transition in the alloy of Ca1-xEuxGa2S4

Room temperature photoluminescence quantum efficiency of the alloy of Ca_1−xEu_xGa₂S₄ was measured as a function of x, and was found to be nearly unity under excitation at peak wavelength of excitation spectrum (510 nm) in the x range of 0.01≤x≤0.2. At larger x values, it tends to decrease, but still as high as 30% for stoichiometric compound EuGa₂S₄. Taking these backgrounds into account, pump-probe experiments were done with Ca_1−xEu_xGa₂S₄ for searching optical gain at x=0.2. The optical gain of nearly 30 cm⁻¹ was confirmed to exist, though the pumping induced transient absorption which seems to limit the higher gain was found.     

Coherence-converted population transfer FTMW-IR double resonance spectroscopy of CH3OD in the OD-stretch region

Rotationally selected infrared spectra of jet-cooled CH₃OD have been recorded and analyzed in the OD-stretch region (2710-2736 cm⁻¹). The observed spectra are obtained by monitoring three E-species microwave transitions (1₋₁ ← 1₀ at 18.957 GHz, 2₋₁ ← 2₀ at 18.991 GHz, and 3₋₁ ← 3₀ at 19.005 GHz) in a narrowband cavity Fourier transform microwave spectrometer, using the background-free coherence-converted population transfer technique. Of the four upper state subbands observed, two (K′ = 0 and −2) are split by perturbations. The E-species deperturbed band origin is at 2718.1 cm⁻¹. The deperturbed reduced term values follow a pattern similar to the ground state. This allows the J′ = 0 torsional tunneling splitting to be estimated as 2.1 cm⁻¹, which can be compared to 2.6 cm⁻¹ in the ground state.     

High-resolution FTIR measurement of the ν4 band of methylene fluoride-d2

A high-resolution (0.002 cm⁻¹) infrared absorption spectrum of methylene fluoride-d₂ (CD₂F₂) of the lowest fundamental mode ν₄ in the region from 460 to 610 cm⁻¹ has been measured on a Bruker IFS 120-HR Fourier transform infrared spectrometer. More than 3500 transitions have been assigned in this B-type band centered at 521.9 cm⁻¹. The data have been combined with upper state pure rotational measurements in a weighted least-squares fit to obtain molecular constants for the upper state resulting in an overall standard deviation of 0.00018 cm⁻¹. Accurate value for the band origin (521.9578036 cm⁻¹) has been obtained and inclusion of transitions with very high J (?60) and K_a (?34) values has resulted in improved precision for sextic centrifugal distortion constants, in particular D_K, H_KJ, and H_K.     

Air-broadened halfwidth and pressure shift coefficients of CO2 bands: 4750-7000 cm

Previously we obtained self-broadened halfwidth and self-induced shift coefficients at room temperature for 15 near infrared CO₂ bands between 4750 and 7000 cm⁻¹ [R.A. Toth, L.R. Brown, C.E. Miller, V.M. Devi, D.C. Benner, J. Mol. Spectrosc., 239 (2006) 243-271]. The present study expands our work on the near infrared line parameters of CO₂ to include air broadening coefficients. Here we report nearly 400 air-broadened half width and air-induced pressure shift coefficients spanning 11 different CO₂ vibrational bands in the 4750-7000 cm⁻¹ region. Retrievals have been performed using Voigt line profiles over three distinct spectral intervals: (a) 4750-5200 cm⁻¹, covering the 20011 ← 00001, 20012 ← 00001, and 20013 ← 00001 Fermi Triad and three associated hot bands 21111 ← 01101, 21112 ← 01101, 21113 ← 01101; (b) 6100-7000 cm⁻¹, covering the 30011 ← 00001, 30012 ← 00001, 30013 ← 00001 and 30014 ← 00001 Fermi Tetrad; (c) near 6950 cm⁻¹ for the 00031 ← 00001 overtone band. The air-broadened halfwidth and air-induced pressure shift coefficients have been modeled with empirical expressions and compared to other measurements available in the literature.     

High resolution analysis of the ν12 and ν17 fundamental bands of acrolein, CH2CHCHO, in the 600 cm region

Synchrotron radiation from the new Canadian Light Source facility has been used to obtain a high resolution (0.0012 cm⁻¹) absorption spectrum of acrolein vapor in the 550-660 cm⁻¹ region. Almost 2000 transitions have been included in a detailed analysis of the ν₁₂ (∼564 cm⁻¹) and ν₁₇ (∼593 cm⁻¹) fundamental bands which yielded precise values for the band origins, rotational and centrifugal distortion parameters. The analysis included the a- and b-type Coriolis interactions connecting ν₁₂ and ν₁₇, as well as an a-type Coriolis interaction between ν₁₇ and a “dark” perturbing state, identified as 4ν₁₈. We believe that this is the first high resolution infrared study of acrolein.     

Spectral manifestations of nonradiative processes in azulene

The linewidths for S₁ ← S₀ (at 14 652 cm⁻¹) and S₂ ← S₀ (at 28 048 cm⁻¹) of azulene in a naphthalene host crystal at 1.2°K are presented along with measurements of the line narrowing due to perdeuteration of the azulene. The results are related to current ideas of nonradiative processes in azulene and azulene-d₈.     

The cavity-enhanced absorption spectrum of NH3 in the near-infrared region between 6850 and 7000 cm

In this paper, we describe new high-resolution measurements of the absorption spectrum of ¹⁴NH₃ in the 6850-7000 cm⁻¹ region using cavity-enhanced absorption spectroscopy (CEAS), and Fourier-transform spectroscopy (FTS) between ∼6400 and 6900 cm⁻¹. The CEAS measurements were used to determine line positions, line intensities (cross-sections) and pressure-broadening parameters, the latter in three different bath gases. A total of 1117 NH₃ lines were observed. The accuracy of the line positions is about 0.001 cm⁻¹, and absorptions cross-sections as low as 1×10⁻²³ cm² molecule⁻¹ are reported.     

One-magnon light scattering and spin-reorientation transition in epitaxial BiFeO3 thin films

Raman scattering from one-magnon excitation has been observed for the first time in epitaxial BiFeO₃ thin films grown on (1 1 1) SrTiO₃ substrates. The intensities and the frequency of the magnon mode at 18.9 cm⁻¹ (M₁) showed a discrepancy at the characteristic temperatures of ∼140 and 200 K and the magnon mode at 27.9 cm⁻¹ (M₂) disappeared at ∼200 K suggesting spin-reorientation (SR) transition in the epitaxial BFO film. The dc susceptibility measurement showed a large discrepancy near these two temperatures evidently elucidating the spin-reorientation transition mechanism. The partial spectral weight of the magnon modes is believed to be transferred to the lowest phonon mode appearing at 72.8 cm⁻¹ and higher magnon mode M₂ disappearing near 200 K reveal magnon-phonon coupling near to SR transition.     

Rovibrational spectrum of the Ne-N2O van der Waals complex in the 1285 cm region

The rovibrational spectrum of the Ne-N₂O van der Waals complex has been recorded in the symmetric stretching mode region of the N₂O monomer (∼1285 cm⁻¹) using a tunable diode laser spectrometer in conjunction with an astigmatic multi-pass cell and a pulsed supersonic slit jet. The spectra of both ²⁰Ne-N₂O and ²²Ne-N₂O isotopomers are assigned and analyzed using a Watson S-reduced asymmetric-rotor Hamiltonian. The rotational and centrifugal constants for the excited vibrational state are accurately determined. The band-origin of the spectrum is determined to be ν₀ = 1285.12251(18) cm⁻¹ for ²⁰Ne-N₂O and 1285.12363(27) cm⁻¹ for ²²Ne-N₂O, which shows a blue-shift of 0.21921 cm⁻¹ for ²⁰Ne-N₂O and 0.22033 cm⁻¹ for ²²Ne-N₂O from that of the N₂O monomer, respectively.     

Infrared absorption and reflectivity of double perovskite Sr2FeWO6

In this work we present temperature dependent infrared reflectivity and absorption of Sr₂FeWO₆ between 700 and 17 K measured from 40 to 10000 cm⁻¹. The reflectivity spectra show well defined phonon bands peaking at 143, 227, 377 and 625 cm⁻¹ assigned to overlapping vibrational modes split from those active in cubic perovskite. We have also verified that this compound is structurally stable in the whole temperature range and that its optical gap at ∼750 cm⁻¹ (95 meV) undergoes only a minor high temperature decrease ascribed to new thermally accessible levels.     

CO2-broadened water in the pure rotation and ν2 fundamental regions

The CO₂-broadened water coefficients (half-widths, line shifts, and temperature dependence of the widths) are predicted using a fully complex Robert-Bonamy formulation for the 937 allowed and forbidden perpendicular type transitions of (000)-(000) between 200 and 900 cm⁻¹ in order to facilitate atmospheric remote sensing of Mars and Venus. In addition, empirical Lorentz line widths and pressure-induced frequency-shifts of CO₂-broadened H₂¹⁶O are obtained at room temperature for 257 perpendicular transitions of the (010)-(000) fundamental. For this, calibrated spectra recorded at 0.0054 cm⁻¹ resolution are measured assuming Voigt line shapes. For transitions between 1287 and 1988 cm⁻¹ with rotational quanta up to J = 13 and K_a = 6, the widths vary from 0.045 to 0.212 cm⁻¹ atm⁻¹ at 300 K; the pressure-shifts are quite large and range from −0.0386 to +0.0436 cm⁻¹ atm⁻¹. For the (010)-(000) band, the RMS and mean observed and calculated differences for CO₂-broadened H₂O half-widths are 12% and −1.9%, respectively, while the RMS and mean ratios of the observed and calculated pressure-induced shift coefficients are 1.6 and 0.79, respectively. For pairs of transitions involving K_a = 0 and 1, such as 2_0 2 ← 3_1 3 and 3_1 3 ← 2_0 2, both the calculated and observed pressure induced shifts in positions are opposite in sign and often similar in magnitude. The data are too limited to characterize vibrational dependencies of the widths, however.     

Ultrafast motion of liquids C2H4Cl2 and C2H4Br2 studied with a femtosecond laser

Transient optical Kerr effect of liquids C₂H₄Cl₂ and C₂H₄Br₂ is investigated, for the first time to our knowledge, with a femtosecond (fs) probe laser delayed with respect to a coherent fs pump laser. Coherent coupling and electronic Kerr signals are observed around zero delay when pump and probe overlap. Persisting after the pump-probe overlap are Kerr signals arising from the torsional and other intramolecular vibrations of the trans and gauche conformations; Kerr signals arising from the intermolecular motion are also observed. Vibrational quantum interference is only observed in liquid C₂H₄Br₂ and the related beats data are fitted with the torsional vibrations, 91 cm⁻¹ (gauche) and 132 cm⁻¹ (trans), and the CCBr angle-bending vibrations, 231 cm⁻¹ (gauche) and 190 cm⁻¹ (trans), with dephasing times, 0.45 ps, 0.45 ps, 2 ps, and 1.5 ps, respectively. These vibrational frequencies agree with those obtained in the frequency-domain. That no vibrational mode is observed for C₂H₄Cl₂ might be attributed to ineffective Raman-pumping. Kerr signals observed after the pump-probe overlap are Fourier transformed to give the spectra of the intermolecular motion and the vibrational spectrum, which agrees with the one observed in the infrared absorption and/or Raman scattering heretofore.     

Intralamellar structural modifications related to the proton exchanging in K4Nb6O17 layered phase

Basic structural aspects about the layered hexaniobate of K₄Nb₆O₁₇ composition and its proton-exchanged form were investigated mainly by spectroscopic techniques. Raman spectra of hydrous K₄Nb₆O₁₇ and H₂K₂Nb₆O₁₇·H₂O show significant modifications in the 950-800 cm⁻¹ region (Nb-O stretching mode of highly distorted NbO₆ octahedra). The band at 900 cm⁻¹ shifts to 940 cm⁻¹ after the replacement of K⁺ ion by proton. Raman spectra of the original materials and the related deuterated samples are similar suggesting that no isotopic effect occurs. Major modifications were observed when H₂K₂Nb₆O₁₇ was dehydrated: the relative intensity of the band at 940 cm⁻¹ decreases and new bands seems to be present at about 860-890 cm⁻¹. The H⁺ ions should be shielded by the hydration sphere what preclude the interaction with the layers. Removing the water molecules, H⁺ ions can establish a strong interaction with oxygen atoms, decreasing the bond order of Nb-O linkage. X-ray absorption near edge structure studies performed at Nb K-edge indicate that the niobium coordination number and oxidation state remain identical after the replacement of potassium by proton. From the refinement of the fine structure, it appears that the Nb-Nb coordination shell is divided into two main contributions of about 0.33 and 0.39 nm, and interestingly the population, i.e., the number of backscattering atoms is inversed between the two hexaniobate materials.     

D2O: ICLAS between 13 600 and 14 020 cm and normal mode labeling of the vibrational states

The high resolution absorption spectrum of dideuterated water, D₂¹⁶O, has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) in the 13 600-14 020 cm⁻¹ spectral region which is the highest energy region reported so far for this water isotopologue. Because the HD¹⁶O absorption is stronger by three orders of magnitude in the region under study, it was necessary to use high deuterium enrichment in order to minimize the HD¹⁶O absorption lines overlapping the D₂¹⁶O spectrum. With the high sensitivity achieved (noise equivalent absorption α_min ∼10⁻⁹ cm⁻¹), transitions with line strengths on the order of 5 × 10⁻²⁸ cm molecule⁻¹ could be detected. The spectrum analysis, based on recent variational calculations has provided a set of 177 new rovibrational energy levels belonging to six vibrational states.The most complete set of 53 vibrational energy levels of D₂¹⁶O, including the three newly determined band origins, was constructed from an exhaustive review of the literature data. The fitting of the parameters of the vibrational effective Hamiltonian has allowed to reproduce the whole set of vibrational energies with an rms deviation of 0.055 cm⁻¹. This simple model gave consistent vibrational labels of the D₂¹⁶O states up to 18 000 cm⁻¹. Above 15 000 cm⁻¹, Fermi and Darling-Dennison resonance interaction were found to induce strong vibrational mixings of the wave functions in the normal mode basis, leading to ambiguous vibrational labeling.     

Luminescence of Ce and Pr doped Sr2Mg(BO3)2 under VUV-UV and X-ray excitation

This report presents the luminescence properties of Ce³⁺ and Pr³⁺ activated Sr₂Mg(BO₃)₂ under VUV-UV and X-ray excitation. The five excitation bands of crystal field split 5d states are observed at about 46 729, 44 643, 41 667, 38 314 and 29 762 cm⁻¹ (i.e. 214, 224, 240, 261 and 336 nm) for Ce³⁺ in the host lattice. The doublet Ce³⁺ 5d→4f emission bands were found at about 25 840 and 24 096 cm⁻¹ (387 and 415 nm). The influence of doping concentration and temperature on the emission characteristics and the decay time of Ce³⁺ in Sr₂Mg(BO₃)₂ were investigated. For Pr³⁺ doped samples, the lowest 5d excitation band was observed at about 42017 cm⁻¹ (238 nm), a dominant band at around 35714 cm⁻¹ (280 nm) and two shoulder bands were seen in the emission spectra. The excitation and emission spectra of Ce³⁺ and Pr³⁺ were compared and discussed. The X-ray excited luminescence studies show that the light yields are ∼3200±230 and ∼1400±100 photons/MeV of absorbed X-ray energy for the samples Sr_1.86Ce_0.07Na_0.07Mg(BO₃)₂ and Sr_1.82Pr_0.09Na_0.09Mg(BO₃)₂ at RT, respectively.     

Intracavity Laser Absorption Spectroscopy of D2O between 12 850 and 13 380 cm

The high resolution absorption spectrum of dideuterated water, D₂O, has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) in the 12 850-13 380 cm⁻¹ spectral region which is the higher energy region reported so far for this water isotopologue. Very high deuterium enrichment was necessary to minimize the HDO absorption lines overlapping the D₂O spectrum. The achieved sensitivity (noise equivalent absorption α_min ∼ 10⁻⁹ cm⁻¹) allowed detecting transitions with line strengths on the order of 5 × 10⁻²⁸ cm/molecule. The spectrum analysis, based on recent variational calculations has provided a set of 422 new rovibrational energy levels belonging to 11 vibrational states, including rotational sublevels for four new vibrational states and one level of the (0 9 1) highly excited bending state. The very weak (1 0 4)-(0 0 0) band at 13 263.902 cm⁻¹, which is the highest D₂¹⁶O band currently observed, could be assigned despite the fact that the HDO absorption in the region is stronger by three orders of magnitude. The list of 996 D₂¹⁶O transitions is provided as Supplementary Material.