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.     

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.     

Sub-Doppler high-resolution excitation spectroscopy of the S1 ← S0 transition of dibenzofuran

Rotationally resolved ultrahigh-resolution fluorescence excitation spectra of the S₁ ← S₀ transition of dibenzofuran have been observed using the technique of crossing a collimated molecular beam and the single-mode UV laser beam. 3291 rotational lines of the band and 3047 rotational lines of the band have been assigned. The band has been found to be a b-type transition, in which the transition moment is along the twofold symmetry axis of this molecule, and only the ΔK_a = ± 1 transitions were observed. The excited state is identified to be the S₁¹A₁(ππ^∗) state. In contrast with this, the band has been found to be an a-type transition in which the transition moment is along the long axis in plane. It indicates that the intensity of this vibronic band arises from vibronic coupling with the S₂¹B₂(ππ^∗) state. We determined the accurate rotational constants and the molecule have been shown to be planar both in the ground and excited states.     

Infrared spectroscopic studies of the rare gas atom perturbed S1(0) rovibron band of solid parahydrogen

We report high resolution infrared absorption studies of rare gas (Rg) atom doped solid parahydrogen in the hydrogen S₁(0) region around 4486 cm⁻¹. At low Rg atom concentrations (∼0.1%), satellite transitions appear in the S₁(0) region due to rovibrational excitation of parahydrogen molecules with one nearest-neighbor Rg atom. The Ne satellite feature differs qualitatively from the Ar, Kr, and Xe satellite features for reasons described within. The frequency of the S₁(0) satellite features linearly shift to lower energy as the polarizability of the Rg atom increases while the absorption coefficients increase with the square of the Rg atom polarizability. Rotational calculations are performed for H₂ with a nearest-neighbor Rg atom assuming a rigid hexagonal close-packed lattice structure. The calculated fine structure of the S₁(0) satellite features agree qualitatively with lifting of the 2J+1 degeneracy of the v = 1, J = 2 upper state caused by the anisotropy in the Rg-H₂ intermolecular potential. The discrepancy between the calculated and measured Rg atom S₁(0) satellite features may signal partial delocalization of the J = 2 roton onto neighboring parahydrogen molecules.     

The 330-nm S1-S0 electronic spectrum of 1-pyrazoline: Probable hindered pseudorotation in S1 and confirmation of the ring-puckering potential function in S0 by single vibronic level fluorescence spectroscopy

The S₁-S₀ absorption spectrum of 1-pyrazoline is rotationally sharp but vibrationally extremely irregular, and other techniques are necessary to aid its assignment. The relaxed fluorescence spectrum shows a very long progression in the NN twisting vibration, suggesting that the ring is twisted in S₁ whereas, in S₀, this part of the ring is planar but the CH₂ group in position 4 is puckered. With a twisted ring in S₁ it seems likely that the NN twisting and CH₂(4) puckering modes in S₀ should be combined and newly described as radial and hindered pseudorotational modes in S₁. The vibronic transitions accompanying such an S₁-S₀ electronic transition are derived. Single vibronic level fluorescence spectra from many vibronic levels of S₁ show progressions in both the NN twisting and CH₂(4) puckering vibrations in S₀, but only with Δv even. This strongly supports the suggestion that these two modes are heavily mixed in S₁, and indicates that the fluorescing states are either above the barrier to pseudorotation or not far below it, so that there is appreciable tunnelling through the barrier. The progressions in the CH₂(4) puckering vibration allow us to assign uniquely the puckering quantum number, in S₀, of the band in which excitation took place. In addition, the spacings in these progressions further confirm the preferred potential function derived from the far-infrared spectrum and confirmed previously from the microwave spectrum.     

The S1−S0 transitions of 1,2,3-trimethylbenzene and 3-fluoro-1,2-dimethylbenzene observed by two-photon spectroscopy

Two-photon (TP)-induced transitions to the ¹L_b state of 1,2,3-trimethylbenzene and 3-fluoro-1,2-dimethylbenzene were studied by resonant multiphoton ionization in a supersonic jet beam. In both molecules the TP S₁ ← S₀ transition has very strong Franck-Condon components and components vibronically induced by ν₁₄. Seven fundamental vibrations of the ¹L_b state are detected in each molecule. A band, which appears near 14₀¹ due to a Fermi resonance, is proposed to be 1₀²15₀¹. The ¹L_b intensity of the heterosubstituted compound is in agreement with the TP orientation intensity rules.     

Rotationally resolved spectroscopy of the ν8 band of cis-methyl nitrite

The 770-880 cm⁻¹ region of the methyl nitrite spectrum has been recorded at a resolution of 0.0015 cm⁻¹ in a static cell. Consistent with published determinations of the barrier to internal rotation of the methyl group, bands belonging to the trans isomer are very congested while those belonging to the cis isomer are more tractable. A total of 634 lines have been assigned in the ν₈ vibrational band of the cis isomer. These lines and 32 microwave lines have been globally fit to a Watson-type Hamiltonian with an rms deviation of 0.00044 cm⁻¹. An additional 150 lines were also assigned but were not included in the fit because they were split by 0.001-0.005 cm⁻¹, much larger than previously reported torsional or hyperfine splittings.     

Ultrahigh-resolution laser spectroscopy of the S1B2u ← S0Ag transition of perylene

A rotationally resolved ultrahigh-resolution fluorescence excitation spectrum of the S₁ ← S₀ transition of perylene has been observed using a collimated supersonic jet technique in conjunction with a single-mode UV laser. We assigned 1568 rotational lines of the band, and accurately determined the rotational constants. The obtained value of inertial defect was positive, accordingly, the perylene molecule is considered to be planar with D_2h symmetry. We determined the geometrical structure in the S₀ state by ab initio theoretical calculation at the RHF/6-311+G(d,p) level, which yielded rotational constant values approximately identical to those obtained experimentally. Zeeman broadening of each rotational line with the external magnetic field was negligibly small, and the mixing with the triplet state was shown to be very small. This evidence indicates that intersystem crossing (ISC) in the S₁¹B_2u state is very slow. The rate of internal conversion (IC) is also inferred to be small because the fluorescence quantum yield is high. The rotational constants of the S₁¹B_2u state were very similar to those of the S₀¹A_g state. The slow internal conversion (IC) at the S₁ zero-vibrational level is attributed to a small structural change upon electronic transition.     

High resolution fourier transform spectrum of PD3 in the region of the stretching overtone bands 2ν1 and ν1+ν3

The infrared spectrum of the PD₃ molecule has been measured in the region of the first stretching overtone bands on a Fourier transform spectrometer with a resolution of 0.0068 cm⁻¹ and analyzed for the first time. More than 800 transitions with J^max=15 have been assigned to the bands 2ν₁ and ν₁+ν₃. An effective Hamiltonian was used which takes into account both the presence of resonance interactions between the states (2 0 0 0) and (1 0 1 0), and interactions of these with the third stretching vibrational state of the v=2 polyad, (0 0 2 0). A set of 44 spectroscopic parameters is obtained from the fit. This reproduces the 305 initial “experimental” upper rovibrational energies with an rms=0.0015 cm⁻¹.     

The far-infrared spectrum of acrolein, CH2CHCHO: The ν18 fundamental and (ν17 + ν18) − ν18 hot bands

The ν₁₈ fundamental band (∼158 cm⁻¹) of acrolein is studied at high resolution (0.0015 cm⁻¹) using synchrotron radiation from the Canadian Light Source facility and a Bruker IFS 125HR Fourier transform spectrometer. By fitting this band, together with some pure rotational transitions, molecular parameters are obtained to accurately determine the energies of the ν₁₈ = 1 state levels for values of (J, K_a) up to at least (45, 24). These parameters should be useful for future high resolution studies of acrolein hot bands. This is demonstrated here by a detailed analysis of the (ν₁₇ + ν₁₈) − ν₁₈ hot band at ∼589 cm⁻¹. The upper state (ν₁₇ + ν₁₈) of this band is found to be perturbed by Coriolis interactions analogous to those affecting the ν₁₇ state.     

New high-resolution analysis of the {ν1 + ν3} band of the NO2 isotopomer of nitrogen dioxide: Line positions and intensities

The high-resolution Fourier transform absorption spectrum of an isotopic sample of nitrogen dioxide, ¹⁵N¹⁶O₂, was recorded in the 3.4 μm region. Starting from the results of a previous study [Y. Hamada, J. Mol. Struct. 242 (1991) 367-377] a new analysis of the ν₁ + ν₃ band located at 2858.7077 cm⁻¹ has been performed. This new assignment concerns (1 0 1) energy levels involving rotational quantum numbers up to K_a = 10 and N = 54. Using a theoretical model which accounts for both the electron spin-rotation resonances within each vibrational state and the Coriolis interactions between the (1 2 0) and (1 0 1) vibrational states, the spin-rotation energy levels of the (1 0 1) vibrational state could be reproduced within their experimental uncertainty. In this way, the precise vibrational energy, rotational, spin-rotation, and coupling constants were achieved for the {(1 2 0), (1 0 1)} interacting states of ¹⁵N¹⁶O₂. Using these parameters and the transition moment operator which was obtained for the main isotopic species, ¹⁴N¹⁶O₂, a comprehensive list of the line positions and intensities was generated for the ν₁ + ν₃ band of ¹⁵N¹⁶O₂.     

The stretching fundamental bands ν1, ν2 and ν4 of HSiD3

The ν₁(A₁), Si-H stretching, ν₂(A₁) and ν₄(E), Si-D stretchings, fundamental bands of HSiD₃ have been recorded at an effective resolution of ca. 0.003 cm⁻¹ between 2080 and 2280 cm⁻¹ and between 1480 and 1720 cm⁻¹, respectively. Ro-vibrational transitions of the H²⁸SiD₃ isotopologue have been assigned in the two spectral ranges, about 700 belonging to ν₁, with J′ up to 25 and K up to 21, and about 1600 to the ν₂/ν₄ dyad, with J′ up to 24 and K′ up to 19. The spectra of all the bands evidence the existence of several perturbations. The transitions of ν₁ have been analyzed either neglecting or including in the model A₁/E Coriolis-type interactions with nearby dark states. The υ₂ = 1 and υ₄ = 1 states have been fitted simultaneously taking into account several ro-vibrational interactions between them and, in addition, with the υ₅ = 2, l = 0 component, and with few other close dark states. The standard deviation of the fit for both ν₁ and the ν₂/ν₄ dyad is, however, more than one order of magnitude larger than the estimated experimental precision and is independent on the adopted model.     

The ν3 and 2ν3 bands of SO3, SO3, SO3, and SO3

This sixth of a series of publications on the high-resolution rotation-vibration spectra of sulfur trioxide reports the results of a systematic study of the ν₃ and 2ν₃ infrared bands of the four symmetric top isotopomers ³²S¹⁶O₃, ³²S¹⁸O₃, ³⁴S¹⁶O₃, and ³⁴S¹⁸O₃. An internal coupling between the l=0(A₁^′) and l=2(E^′) levels of the 2ν₃ states was observed. This small perturbation results in a level crossing between |k−l|=9 and 12, in consequence of which the band origins of the A₁^′,l=0 “ghost” states could be determined to a high degree of accuracy. Ground and upper state rotational constants as well as vibrational anharmonicity constants are reported. The constants for the center-of-mass substituted species ³²S¹⁶O₃ and ³⁴S¹⁶O₃ vary only slightly, as do the constants for the ³²S¹⁸O₃, ³⁴S¹⁸O₃ pair. The S-O bond lengths for the vibrational ground states of the species ³²S¹⁶O₃, ³⁴S¹⁶O₃, ³²S¹⁸O₃, and ³⁴S¹⁸O₃ are, respectively, 141.981 99(1), 141.979 38(6), 141.972 78(8), and 141.969 93(8) pm, where the uncertainties, given in parentheses, are two standard deviations and refer to the last digits of the associated quantity.     

Rotational analysis of the ν1, 2ν1 and 5ν1 stretching bands of HGeD3

The high-resolution spectrum of the ν₁=5 stretching overtone of gaseous H⁷⁰GeD₃ has been recorded by an intracavity laser absorption spectrometer based on a vertical external cavity surface emitting laser (VECSEL). The rotational structure of the excited state at 9874.605 cm⁻¹ was found weakly perturbed by unidentified interaction with dark states. Finally, of the 313 lines rotationally assigned, 239 lines were found unperturbed and could be reproduced with a root-mean-square (rms) deviation of 0.012 cm⁻¹. The retrieved set of rotational parameters agrees with the values extrapolated from the previously studied ν₁=6-8 stretching overtones. High-resolution FTIR spectra of the ν₁ and 2ν₁ bands have also been recorded and analyzed. The ν₁=1 level, (ν_eff=2114.15 cm⁻¹) is in anharmonic interaction with a further A₁ symmetry level (ν_eff=2102.39 cm⁻¹). The potential coupling term could be estimated (W_anh=5.6(3) cm⁻¹) and the most probable assignment of the perturber is ν₂+ν₃. Moreover both levels are rotationally perturbed in an irregular fashion. Only a coarse analysis up to J=6 could be performed. The 2ν₁ band reveals irregular perturbations of medium intensity by unknown dark states for almost all K values. Nevertheless the obtained leading rovibrational parameters of the 2ν₁ band for J?6 are in agreement with those of the ν₁=5-8 states.     

The rotational spectrum of BiO radical in its X1Π1/2 and X2Π3/2 states

Rotational spectra have been observed for BiO produced in a DC discharge through a low pressure mixture of O₂, Ar, and Bi vapor. Because of the highly non-thermal distribution of states, it has been possible to observe spectra arising from the X₁²Π_1/2 level up to v = 9 and for the X₂²Π_3/2 level up to v = 5 near 10 538 cm⁻¹. Precise rotational and hyperfine parameters have been determined for the observed states. By using available near infrared (NIR) data in a merged fit, the 0-0 and 1-1 fine structure intervals have been more precisely determined. Although the quality of the fit is very good, the interpretation of the hyperfine constants is complicated by relativistic effects and the interaction of the X₂ state with A₁⁴Π_3/2 state. The magnetic and quadrupole coupling constants will be compared with those of the Bi atom and related molecules.     

Analysis of FTIR spectra of CH2BrCl; the ν4 and ν5 fundamentals and their hot-bands ν4+ν6−ν6 and ν5+ν6−ν6

The infrared spectrum of isotopically pure CH₂⁷⁹BrCl has been recorded at a resolution of 0.0023 cm⁻¹ (FWHM) in the range 550-800 cm⁻¹ with a Bruker IFS 120 HR Fourier transform spectrometer in Wuppertal. Here we report the full rotational analysis of the ν₄ and ν₅ fundamentals and of the hot-bands ν₄+ν₆−ν₆ and ν₅+ν₆−ν₆. Ground state combination differences were constructed for all bands, yielding improved ground state constants, up to quartic terms, as well as reliable rotational constants for the ν₄, ν₅, and ν₆ states.     

The ν1 + 3ν2 + 3ν3 and 4ν1 + ν2 + ν3 bands of ozone by CW-cavity ring down spectroscopy between 5900 and 5960 cm

The absorption spectrum of ozone, ¹⁶O₃, has been recorded in the 5903-5960 cm⁻¹ region by high sensitivity CW-cavity ring down spectroscopy (α_min ∼ 5 × 10⁻¹⁰ cm⁻¹). The ν₁ + 3ν₂ + 3ν₃ and 4ν₁ + ν₂ + ν₃ A-type bands centred at 5919.15 and 5947.07 cm⁻¹ were newly observed. A set of 173 and 168 energy levels could be experimentally determined for the (1 3 3) and (4 1 1) states, respectively. Except for a few K_a = 5 levels of the (4 1 1) state, the rotational structure of the two states was found mostly unperturbed. The spectroscopic parameters were determined from a fit of the corresponding line positions by considering the (1 3 3) and (4 1 1) states as isolated. The determined effective Hamiltonian and transition moment operators were used to generate a list of 785 transitions given as Supplementary Material.     

Antiferromagnetic resonance in ferroborate NdFe3(BO3)4

The AFMR spectra of the NdFe₃(BO₃)₄ crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of its magnetic anisotropy the compound is an “easy-plane” antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields H_a1=1.14 kOe and H_a2=60 kOe and magnetic excitation gaps Δν₁=101.9 GHz and Δν₂=23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width.At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed.     

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.     

Fabrication and characterization of epitaxial Sr0.6Ba0.4Nb2O6/La0.7Sr0.3CoO3 heterostructures

Epitaxial Sr_0.6Ba_0.4Nb₂O₆(SBN60)/La_0.7Sr_0.3CoO₃ heterostructures were fabricated on LAO(0 0 1) substrates using pulsed laser deposition (PLD). Their structural properties were investigated by X-ray diffraction. The θ-2θ scans showed single crystalline Sr_1−xBa_xNb₂O₆ (SBN) and La_xSr_1−xCoO₃ (LSCO) layers with a 〈0 0 1〉 orientations perpendicular to the substrate plane. Phi scans on the (2 2 1) plane of SBN layer indicated that the films have two in-plane orientations with respect to the substrate. The SBN unit cells were rotated in the plane of the film by ±18.4° as well as ±45° with respect to the LAO substrate. This rotation was explained by considering the lattice matching between films and substrate, and minimization of electrostatic energy. Spectroellipsometry (SE) was used to characterize the depth profile, the microstructural inhomogeneities, including voids and surface roughness, refractive indices and extinction coefficients of the films.