Fourier transform microwave spectroscopy of the reactive intermediate monoiodosilylene,HSiI and DSiI

The pure rotational spectra of three silicon isotopologues of HSiI and two isotopologues of DSiI have been recorded by pulsed-jet Fourier transform microwave (FTMW) spectroscopy. Neon was passed over dry ice cooled H₃SiI or D₃SiI and introduced into the pulsed valve of the FTMW spectrometer. The monoiodosilylenes HSiI and DSiI were produced in situ with a 1000 V DC-discharge nozzle. Only a-type transitions occur in monoiodosilylene from 6 to 26 GHz. We observe K_a = 0 a-type transitions for H²⁸SiI, H²⁹SiI, H³⁰SiI, and D²⁹SiI, and both K_a = 0 and 1 a-type transitions for D²⁸SiI. Rotational constants, centrifugal distortion constants, iodine nuclear quadrupole coupling constants, and nuclear spin–molecular rotation constants were measured.     

Infrared spectroscopy of superionic conductor LiNaSO4: Vibrational modes and thermodynamics

Infrared active phonon spectra of lithium sodium sulphate, LiNaSO₄, were studied at temperatures between 20 K and 780 K. Dielectric constant [ε = ε′ + iε″] and energy loss function [− Im(1/ε)] were obtained from Kramers–Kronig analysis. Our IR data show a more complete set of vibrational modes than previous investigations. The IR data of LiNaSO₄ at 20 K are consistent with the P31c symmetry, indicating that LiNaSO₄ shows no structural phase transitions between 20 K and 300 K, in contrast to LiKSO₄. On heating from 20 K, phonon modes related to Li and Na vibrations show a dramatic line broadening and decrease in intensity. An extra mode is recorded near 380 cm^− 1 at 500 K. The absorption shows a systematic increase in intensity on further heating. These changes are attributed to anharmonic effects and Li diffusion or hopping. Dramatic spectral changes in the internal modes occur near 620 K on heating, suggesting the onset of the rotational disorder of SO₄ tetrahedra, but the Li atom spectrum shows weak response to the rotational disorder.     

Frequency and intensity analyses of the far infrared ν5 band system of cyanogen (C2N2) and applications to Titan

The far infrared spectrum of cyanogen has been studied at high resolution to improve the rotational analysis of the ν₅ band system around 234 cm^?1. Present in the sample in natural abundances, both isotopologues N¹³CCN and ¹⁵NCCN have also been studied. The weak ν₄–ν₅ difference band centered at 270 cm^?1 has been studied for the first time. On the basis of a global rovibrational analysis limited to the ν₂, ν₄, and ν₅ modes, energy levels up to 2300 cm^?1 have been considered to contribute to the overall spectrum intensity at room temperature leading to a new line list of 196,994 lines. The line intensity prediction has been used to correct previous line intensity measurements by taking into account line mixing. A new vibrational transition moment has been deduced and compared to new band intensity measurements obtained by low resolution studies which are also presented in this paper. The agreement between both approaches is very good and rules out the apparent disagreement between line intensity and band intensity measurements observed in the past. An intensity study of ¹⁵NCCN is also proposed here thanks to the availability of a pure sample. Those results open the way to the search for isotopologues of cyanogen in Titan's atmosphere.     

Microwave observation of 41K79Br and 41K81Br from laser-ablated potassium bromide

The J = 2 ← 1 transitions of the previously unobserved isotopologues ⁴¹K⁷⁹Br and ⁴¹K⁸¹Br have been recorded with a pulsed-nozzle Fourier transform microwave spectrometer, newly combined with a 532 nm laser ablation source. Aspects of the experimental design are described. Rotational and nuclear quadrupole coupling constants are obtained and combined with published results for ³⁹K⁷⁹Br and ³⁹K⁸¹Br to produce a set of isotopically invariant parameters. New rotational transitions of ²³Na^35,37Cl, ³⁹K⁷⁹Br, and ³⁹K¹²⁷I have also been recorded. Excited vibrational states are not observed, indicating efficient cooling of the metal halides following the initial ablation event.     

Rotational analysis of bands in the high-resolution infrared spectra of cis,cis- and trans,trans-1,4-difluorobutadiene-2-d1

Pure samples of cis,cis- and trans,trans-1,4-difluorobutadiene-2-d₁ have been synthesized, and high-resolution (0.0015 cm^?1) infrared spectra have been recorded for these nonpolar molecules in the gas phase. For the cis,cis isomer, the rotational structure in two C-type bands at 775 and 666 cm^?1 and one A-type band at 866 cm^?1 has been analyzed to yield a combined set of 2020 ground state combination differences (GSCDs). Ground state rotational constants fit to these GSCDs are A₀ = 0.4195790(4), B₀ = 0.0536508(8), and C₀ = 0.0475802(9) cm^?1. For the trans,trans isomer, three C-type bands at 856, 839, and 709 cm^?1 have been investigated to give a combined set of 1624 GSCDs. Resulting ground state rotational constants for this isomer are A₀ = 0.9390117(8), B₀ = 0.0389225(4), and C₀ = 0.0373778(3) cm^?1. Small inertial defects confirm the planarity of both isomers in the ground state. Upper state rotational constants have been determined for most of the transitions. The ground state rotational constants for the two isotopologues will contribute to the data set needed for determining semiexperimental equilibrium structures for the nonpolar isomers of 1,4-difluorobutadiene.     

High sensitivity CW-Cavity Ring Down Spectroscopy of N2O between 6950 and 7653 cm−1 (1.44–1.31 μm): I. Line positions

The absorption spectrum of nitrous oxide, N₂O, has been recorded by CW-Cavity Ring Down Spectroscopy between 6950 and 7653 cm^?1. The spectra were obtained at Doppler limited resolution using a CW-CRDS spectrometer based on a series of fibered DFB laser diodes. The typical noise equivalent absorption, in the order of α_min≈1×10^?10 cm^?1, allowed for the detection of lines with intensity as small as 1×10^–29 cm/molecule.The positions of 7203 lines of four isotopologues (¹⁴N₂¹⁶O, ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O and ¹⁴N₂¹⁸O) were measured with a typical accuracy of 1.0×10^?3 cm^?1. The transitions were rovibrationally assigned on the basis of the global effective Hamiltonian models developed for each isotopologue. The band by band analysis allowed for the determination of the rovibrational parameters of more than 95 bands, most of them being newly reported while new rotational transitions are measured for the others. The measured line positions of the main isotopologue are found to be in good agreement with the predictions of the effective Hamiltonian model but a few deviations up to 0.20 cm^?1 are observed. Local rovibrational perturbations were evidenced for several bands. The interaction mechanisms and the perturbers were univocally assigned on the basis of the effective Hamiltonian models.     

Improved measurements and analysis of the far-infrared spectrum of methanol-D1 (CH2DOH) arising from trans- (e0) to gauche- (e1 & o1) states

In this work the millimeter-wave (MMW) and far infrared (FIR) absorption spectrum for the asymmetrically deuterated Methanol (CH₂DOH) species measured recently at a temperature of −60 °C with better accuracy and signal/noise (S/N) ratio than known before has been assigned for transitions originating at the lowest lying trans- to gauche-states. The entire spectrum for 50–1200 cm⁻¹ has been re-recorded recently using the Synchrotron Radiation Source coupled with the Bruker Fourier Transform Infrared (FTIR) spectrometer with a resolution of about 0.001 cm⁻¹ or better. Complete spectrum has not been exploited a great deal but it helped to entangle overlapping lines in the present work. This also fills the gap remaining in the usual FTIR in the range 400–500 cm⁻¹. Hence it is expected to help the interacting partner for the Coriolis interaction encountered earlier. The assigned transitions mostly for the axial rotational angular momentum quantum number K + 1 ← K, both for R- and Q-sub bands for wide range of rotational angular momentum quantum number. The MMW spectrum has been recalibrated and assigned for a number of Q-branches. The assignments are confirmed rigorously using closed loop residual technique. The assigned ^rR and ^rQ lines have been analyzed in terms of polynomial expansion parameters. The new assignments are presented for about 750 transitions and a grand atlas of more than 1000 lines has been prepared which will be made available through the open source server at “research gate”. The present work should be useful in the area of astrophysical detection and further understanding of the energy relaxation pathways in the molecule.     

Millimetre-wave spectrum of anti-13C1 and 13C2 isotopologues of ethanol

The rotational spectra of the two monosubstituted ¹³C isotopologues of the anti conformer of ethanol have been measured between 80–800 GHz using three different spectrometers at the Cologne Laboratory Astrophysics group. The dataset was constrained for fitting with a standard Watson-S reduction Hamiltonian by rejecting transitions from high-lying states showing significant perturbation with the gauche states and by averaging some small methyl torsional splits. This treatment is compatible with the needs for a first astrophysical research for which an appropriate set of predictions is given.     

Electronic excitations and luminescence of SrAlF5 crystals doped with Ce3+ ions

This paper reports the results of a time-resolved photoluminescence and energy transfer processes study in Ce³⁺ doped SrAlF₅ single crystals. Several Ce³⁺ centers emitting near 4 eV due to 5d-4f transitions of Ce³⁺ ions substituting for Sr²⁺ in non-equivalent lattice sites were identified. The lifetime of these transitions is in the range of 25–35 ns under intra-center excitation in the energy region of 4–7 eV at T = 10 K. An effective energy transfer from lattice defects to dopant ions was revealed in the – 7–11 eV energy range. Both direct and indirect excitation channels are efficient at room temperature. Excitons bound to dopants are revealed at T = 10 K under excitation in the fundamental absorption region above 11 eV, as well as radiative decay of self-trapped excitons resulting in luminescence near 3 eV.     

7Li and 51V NMR study on Li+ ionic diffusion in lithium intercalated LixV2O5

Li_xV₂O₅ (0.4 < x < 1.4) prepared by solid-state reaction were studied by ⁷Li and ⁵¹V NMR spectroscopy. ⁷Li NMR spectra showed a narrowing of the line width in relation to Li⁺ionic diffusion. Analysis of Li_xV₂O₅ using a Debye-type relaxation model showed a low activation energy ∼0.07 eV in the sample of x = 0.4 below room temperature, and revealed a Li⁺ionic diffusion with larger activation energy ∼0.5 eV above 450 K in lithium-rich samples. The latter is ascribed to the existence of a multi-phase system comprising stable ɛ- and γ-phases, resulting from complicated phase transitions at high temperature. These shapes and shifts enable the classification of the β-, ɛ-, δ-, and γ-phases. The ionic diffusion of Li⁺ ions is discussed in relation to the complicated phase transitions.     

Photoionization studies of the atmospherically important species N and OH at the Elettra synchrotron radiation source

In this paper angularly resolved photoelectron spectra (PES) and constant-ionic-state (CIS) spectra are presented for the atmospherically important species N and OH.The natural width Γ, line shape parameters q and ρ² and discrete oscillator strengths f have been measured for the members of the N*[2s2p³(⁵S), np] (⁴P) ← N(⁴S) autoionizing resonances for n = 5–10. The n = 5 parameters calculated in this work are in good agreement with the values obtained previously whereas for the resonances with n = 6–10 the values of these parameters are reported for the first time. The asymmetry parameter (β) for the first band of N atoms, the N⁺(³P) ← N(⁴S) ionization, has also been measured in the photon energy range of the above autoionizing resonances.For OH, CIS spectra have been recorded for the first photoelectron band corresponding to the ionization OH⁺(X³Σ⁻, v⁺ = 0) ← OH(X²Π, v″ = 0). In these spectra, rotationally partially resolved bands associated with OH*(a¹Δ3d, v′ = 0) ← OH(X²Π, v″ = 0) resonances have been observed. Suggestions for their assignment are made on the basis of their positions and band simulations which use rotational line strength calculations.     

Hole polaron of small radius in assemblies of hydrated mono-protonated meso-tetraphenylporphine dimers at 77 K

Polaron theory is often used for the study of electrons and holes mobility in semiconductors when longitudinal optical (LO) phonons are generated upon the charge carriers moving. The polaron theory was applied to explain long-wavelength absorptions observed nearby Soret band in the electronic spectra of assemblies of mono-protonated meso-tetraphenylporphine dimer (TPP₂H⁺) that are interpreted as LO-phonons originated due to proton movement. The energy of hole polaron is found to be 1.50 eV at 77 K. Energy of Franck–Condon transitions of LO-phonons generated by hole polaron moving through water confined in the assemblies with distortions of O–H bonds is 0.2653 eV (2138 cm⁻¹). A broad band around 2127 cm⁻¹ corresponding the same energy of O–H bonds vibrations is observed in IR spectra of the assemblies consisting of water and mainly of TPP₂H⁺ species in the solid state indicating the presence of similar distortions of the hydrogen bonds. The radius of protonic sphere of 0.202 Å, which was estimated as a polaron quasiparticle moving through the confined water at 77 K, is found in agreement with earlier evaluated one of 0.265 Å that was obtained for proton diffusion at 298 K in similar assemblies.     

Volumetric properties and viscosities of the 2-pyrrolidone + 1,2-propanediol + water ternary system and its binary constituents at T = 313.15 K

Densities and viscosities of ternary mixtures of 2-pyrrolidone + 1,2-propanediol + water and corresponding binary mixtures of 1,2-propanediol + water, 2-pyrrolidone + water and 2-pyrrolidone + 1,2-propanediol have been measured over the whole composition range at 313.15 K. From the obtained data, the excess molar volumes (V^E), the deviations in viscosity (Δη) and the excess Gibbs free energy of activation (ΔG^?E) have been calculated. The V^E, Δη and ΔG^?E results were correlated and fitted by the Redlich–Kister equation for binary mixtures and by the Cibulka equation for ternary mixtures, as a function of mole fraction. Several predictive empirical relations were applied to predict the excess molar volumes of ternary mixtures from the binary mixing data.     

The far infrared spectrum of trans-formic acid: An extension up to 175 cm−1

The far infrared spectrum of HCOOH was recorded at a high resolution (0.0009 cm^?1) and long path length (72 m) at the far-infrared beamline, Canadian Light Source. Spectra were recorded in the region 62–300 cm^?1, showing transitions from the trans-isomer.Ground state rotational transitions with K_a up to 30, were identified up to 175 cm^?1, extending the observation reported in the literature. A total of 3321 transitions were assigned and fitted together with previous (4149) published data. An improved set of rotational parameters was obtained adopting the symmetric top (A) reduction of the rotational Hamiltonian in the I^r representation. The newly measured far infrared transitions allowed the determination of all diagonal and off diagonal 8th order parameters L and of some of the diagonal 10th order parameters P.     

High resolution emission spectroscopy of the E2Π–X2Σ+ transition of SrH and SrD

Emission spectra of SrH and SrD have been studied at high resolution using a Fourier transform spectrometer. The molecules have been produced in a high temperature furnace from the reaction of strontium metal vapor with H₂/D₂ in the presence of a slow flow of Ar gas. The spectra observed in the 18 000–19 500 cm^?1 region consist of the 0–0 and 1–1 bands of the E²Π–X²Σ⁺ transition of the two isotopologues. A rotational analysis of these bands has been obtained by combining the present measurements with previously available pure rotation and vibration–rotation measurements for the ground state, and improved spectroscopic constants have been obtained for the E²Π state. The present analysis provides spectroscopic constants for the E²Π state as ΔG(½) = 1166.1011(15) cm^?1, B_e = 3.805503(32) cm^?1, α_e = 0.098880(47) cm^?1, r_e = 2.1083727(89) Å for SrH, and ΔG(½) = 839.1283(23) cm^?1, B_e = 1.918564(15) cm^?1, α_e = 0.034719(23) cm^?1, r_e = 2.1121943(83) Å for SrD.     

The absorption spectrum of methane at 80 and 294 K in the icosad (6717–7589 cm−1): Improved empirical line lists,isotopologue identification and temperature dependence

Using a cryogenic cell and a series of Distributed Feed Back (DFB) diode lasers, new high resolution spectra of methane have been recorded at 80 K and room temperature by differential absorption spectroscopy (DAS) between 6717 and 7589 cm^?1 (1.49–1.32 μm). The investigated spectral region corresponds to the very congested icosad, which is not tractable by theory. Empirical lists of 19,940 and 24,001 lines were constructed from the 80 K and room temperature spectrum, respectively. The room temperature list adds about 8500 features to the empirical list of 15,375 lines at 296 K adopted in the HITRAN database from the original work of L. Brown (Brown, L. Empirical line parameters of methane from 1.1 to 2.1 μm. JQSRT 2005;96:251–70). A number of relatively strong CH₄ lines located near strong water lines were found missing in the HITRAN line list. The improved sensitivity allowed adding more than 7000 lines to our previous list of about 12,000 transitions at 80 K (Campargue A, Wang L, Kassi S, Ma?át M, Votava O. Temperature dependence of the absorption spectrum of CH₄ by high resolution spectroscopy at 81 K: (II) The Icosad region (1.49–1.30 μm). JQSRT 2010;111:1141–51). In order to facilitate identification of the transitions of the different methane isotopologues present in “natural” isotopic abundance, spectra of highly enriched CH₃D and ¹³CH₄ samples were recorded with the same experimental setup, both at room temperature and at 80 K.From the variation of the line strengths between 80 K and 294 K, the low energy values of about 12,000 transitions were determined. They allow accounting for the temperature dependence of 84 and 93% of the methane absorbance in the region, at room temperature and 80 K, respectively. As a result, we provide as supplementary material two complete line lists at 80 K and 294 K, including CH₃D and ¹³CH₄ identification and lower state energy values.     

CRDS of water vapor at 0.1 Torr between 6886 and 7406 cm−1

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) between 6885.79 and 7405.91 cm^?1. This strong absorbing region includes the first hexad of interacting vibrational bands which was previously studied by Fourier Transform Spectroscopy. The achieved sensitivity of the recordings varies from α_min～2×10^–11 to 2×10^?10 cm^?1 allowing us to use a sample pressure of 0.1 Torr, making pressure broadening of the line profile mostly negligible. Weak lines in the vicinity of much stronger lines could then be accurately measured. The weakest lines have intensity on the order of 5×10^–28 cm/molecule at 296 K. A set of 4471 lines were assigned to 4916 transitions of five water isotopologues (H₂ ¹⁶O, H₂ ¹⁸O, H₂ ¹⁷O, HD¹⁶O and HD¹⁸O). A small number of new energy levels was determined mostly for the H₂ ¹⁷O isotopologue. The previous investigations and existing databases are critically evaluated. In particular, a number of corrections and new assignments are proposed for the water list provided by the HITRAN database in the considered region. As a result, a complete list of 12,700 transitions for water in “natural” isotopic abundance is provided as Supplementary Material for the 6885–7408 cm^?1 region.     

Refinements of the WKMC empirical line lists (5852–7919 cm−1) for methane between 80 K and 296 K

During the last 4 years, empirical line lists for methane at room temperature and at 80 K were constructed from spectra recorded by (i) differential absorption spectroscopy (DAS) in the high energy part of the tetradecad (5852?6195 cm^?1) and in the icosad (6717–7589 cm^?1) and (ii) high sensitivity CW-Cavity Ring Down Spectroscopy (CRDS) in the 1.58 μm and 1.28 μm transparency windows (6165–6750 cm^?1 and 7541–7919 cm^?1, respectively). We have recently constructed the global line lists for methane in “natural” isotopic abundance, covering the spectral region from 5854 to 7919 cm^?1 (Campargue A, Wang L, Kassi S, Mondelain D, Bézard B, Lellouch E, et al., An empirical line list for methane in the 1.26–1.71 μm region for planetary investigations (T=80–300 K). Application to Titan, Icarus 219 (2012) 110–128). These WKMC (Wang, Kassi, Mondelain, Campargue) empirical lists include about 43,000 and 46,420 lines at 80±3 K and 296±3 K, respectively. The “two temperature method” provided lower state energy values, E_emp, for about 24,000 transitions allowing us to account satisfactorily for the temperature dependence of the methane absorption over the considered region. The obtained lists have been already successfully applied in a large range of temperature conditions existing on Titan, Uranus, Pluto, Saturn and Jupiter.In the present contribution, we provide some improvements to our lists by using literature data to extend the set of lower state energy values and by correcting the distortion of the high E_emp values (J>10) due to the temperature gradient existing in the cryogenic cell used for the recordings. The proposed refinements are found to have an overall limited impact but they may be significant in some spectral intervals below 6500 cm^?1.The new version of our lists at 80 K and 296 K is provided as Supplementary Material: the WKMC@80K+ and WKMC@296K lists are adapted for planetary and atmospheric applications, respectively. The WKMC@80K+ list is made applicable over a wider range of temperatures and shows satisfactory extrapolation capabilities up to room temperature. It was obtained by transferring to the 80 K list the 27,580 single lines present only in the 296 K list, with corresponding lower state energy values chosen to make them below the detectivity limit at 80 K.In the discussion, the different line lists and databases available for methane in the near infrared are compared and some suggestions are given.     

Analysis of the Coriolis interaction between ν6 and ν4 bands of ethylene-cis-d2(cis-C2H2D2) by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of the ν₆ band of ethylene-cis-d₂(cis-C₂H₂D₂) was recorded with a unapodized resolution of 0.0063 cm^?1 in the 990–1100 cm^?1 region. A total of 609 transitions were assigned to this band centred at 1039.7682 ± 0.0003 cm^?1. The ν₆ band was found to be coupled to the ν₄ band by a-type Coriolis resonance. Both perturbed and unperturbed transitions were assigned and fitted to give eight rovibrational constants with high accuracy for the v₆ = 1 state with a standard deviation of 0.00097 cm^?1 using a Watson’s A-reduced Hamiltonian in the I^r representation. From a rovibrational analysis of the Coriolis interaction between the ν₆ band and non-infrared active ν₄ band of cis-C₂H₂D₂, the band centre of ν₄ at 984.9 ± 0.2 cm^?1 was derived. Furthermore, the second-order a-type Coriolis coupling constant between the two bands was obtained for the first time.     

Detection and analysis of four new bands in CRDS 16O3 spectra between 7300 and 7600 cm−1

The absorption spectrum of the ¹⁶O₃ isotopologue of ozone was recorded in the 7000–7920 cm^?1 region by using high sensitivity CW-Cavity Ring Down Spectroscopy (α_min ～ 10^?10 cm^?1). This report is devoted to the analysis of the 7300–7600 cm^?1 region dominated by four A-type bands: 6ν₁ + ν₃ centred around 7395 cm^?1, 3ν₁ + 5ν₂ + ν₃ and 2ν₁ + 4ν₂ + 3ν₃ lying in the 7450 cm^?1 region and 5ν₁ + 2ν₂ + ν₃ centred around 7579 cm^?1. 213 transitions of the 6ν₁ + ν₃ band were assigned and the corresponding line positions were modeled using an effective Hamiltonian including a Coriolis resonance interaction between the (601) upper state and a A-type dark state. The two very close 3ν₁ + 5ν₂ + ν₃ and 2ν₁ + 4ν₂ + 3ν₃ bands were analysed using a similar effective Hamiltonian scheme involving the anharmonic resonance coupling between the (351) and (243) states. For these two bands, 304 transitions were assigned. The modelling also includes a first Coriolis resonance interaction between the (351) bright state and the (530) dark state, and a second one between the (243) bright state and the (144) dark state. In the 7579 cm^?1 region, 205 transitions of the 5ν₁ + 2ν₂ + ν₃ band were assigned and modelled taking into account the Coriolis resonance interactions between the (521) upper state and the (700), (342) and (280) dark states.The dipole transition moment parameters of the four analysed bands were determined by a least-squares fit to the measured line intensities. For the studied band systems, the effective Hamiltonian and transition moment operator parameters were used to generate line lists provided as Supplementary Materials.