Hydrogen line broadening in the ν2 and ν4 bands of phosphine at low temperature

Using a tunable diode-laser spectrometer, we have measured H₂-broadening coefficients of PH₃ at low temperature (173.2 K) for 27 lines in the ^QR branch of the ν₂ band and in the ^PP and ^RP branches of the ν₄ band. The recorded lines with J values ranging from 2 to 11 and K from 0 to 9 are located between 1016 and 1093 cm⁻¹. The collisional widths are determined by fitting each spectral line with a Voigt profile and a speed-dependent Rautian profile which provides slightly larger broadening coefficients than the Voigt model. These coefficients have also been calculated on the basis of a semiclassical model of interacting linear molecules by considering an atom-atom Lennard-Jones potential in addition to the weak electrostatic contributions. Except for three ^QR(J,K) lines, where K = J, the calculated broadening coefficients are in good agreement with the experimental data. By comparing the results obtained at room and low temperatures, the temperature dependence of linewidths has been determined both theoretically and experimentally.     

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.     

S0 and S1 spectroscopy of jet cooled 9-cyano-10-methylanthracene: The methyl group as a molecular rotor

Jet-cooled fluorescence excitation and dispersed fluorescence spectra of 9-methylanthracene (MA), 9-cyanoanthracene (CA) and 9-cyano-10-methylanthracene (CMA) have been measured. The spectra of MA and CMA near the S₀-S₁ origin reveal a prominent torsional progression due to the hindered methyl group rotation and its torsional vibration against the aromatic ring frame. Additionally, the laser induced fluorescence LIF excitation spectrum of CMA shows the splitting of many vibrational modes.Observed positions and relative intensities of the methyl internal rotational bands were interpreted in terms of transitions calculated based on the quantum mechanical one-dimensional rotor. The low-frequency vibrational bands were interpreted also with the all electron quantum mechanical calculations within the RHF/6-31G(d,p), CIS/3-21G and CIS/6-31G(d,p) approximations. It is predicted that in the case of MA the eclipsed geometry (one C-H in the plane of the ring) is most stable in both S₀ and S₁ states. Conformation of the methyl group in CMA is suggested to change upon S₁ ← S₀ excitation (π/12 phase shift of the methyl group). The predicted energy barrier for methyl group rotation in the S₀ state of CMA is considerably higher (72 cm⁻¹) than that in the S₁ state (22 cm⁻¹). Following the present quantum mechanical calculations, the carbon atom of the methyl group belongs to the aromatic plane in the S₀ ground state but it deviates from this plane in the S₁ excited state. These in turn suggest that the calculated barrier for methyl group rotation in CMA has a 6-fold symmetry in the S₀ ground state and roughly a 4-fold symmetry in the S₁ state.     

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.     

High resolution infrared spectra of the ν1-ν4 bands of BiH3, and ab initio calculations of the spectroscopic parameters

The infrared spectrum of short-lived BiH₃ has been studied by Fourier transform technique. The BiH stretching bands ν₁/ν₃ at 1733.2546/1734.4671 cm⁻¹ and the bending fundamentals ν₂/ν₄ at 726.6992/751.2385 cm⁻¹ have been measured with a resolution of 5.5 and 6.6 × 10⁻³ cm⁻¹, respectively. The spectra were analyzed using different reductions of the rovibrational Hamiltonian accounting for the numerous resonance interactions in particular within the strongly Coriolis-coupled bending dyad. About 1150 and 980 transitions belonging to the ν₁/ν₃ and ν₂/ν₄ bands were fitted with an rms deviation of 0.62 and 0.53 × 10⁻³ cm⁻¹, respectively. High-level ab initio calculations at the coupled cluster CCSD(T) level with an energy-consistent small-core pseudopotential and large basis sets were carried out to determine the equilibrium structure, the anharmonic force field, and the associated spectroscopic constants of BiH₃. The theoretical results are in good agreement with the available experimental data.     

Line profile study by diode laser spectroscopy in the CH4ν2 + ν4 band

We present a complete study on four methane lines for two atmospheric micro-windows (in the ν₂ + ν₄ absorption band) used for the determination of atmospheric methane concentrations with ground-based Fourier transform spectrometers. Thanks to our tunable diode laser (TDL) spectrometer with active wavenumber control and step-by-step recording mode we have improved the accuracy on intensity, broadening, narrowing, and pressure shift parameters. To make our results directly useable in atmospheric models which usually assume a Voigt line shape, we have parameterised an effective-broadening parameter γ_Voigt (P) for each line and each gas mixture (CH₄-N₂ and CH₄-O₂). When this parameterisation is used to fit a “true” line profile, the same concentration as with more sophisticated models is retrieved using a consistent set of spectroscopic parameters in both approaches.     

Doppler-limited CW infrared cavity ringdown spectroscopy of the ν1+ν3 OH + CH stretch combination band of jet-cooled methanol

A high resolution cavity ringdown spectrometer (CRDS) has been constructed using a 1.5 μm continuous-wave external-cavity tunable diode laser, a mode-matched near-confocal ringdown cavity, and 2 cm pulsed slit jet. Without signal averaging, the RMS noise in the absorption signal is 1.7 × 10⁻⁹ cm⁻¹. The rotationally resolved overtone spectrum of the OH(ν₁) + CH(ν₃) stretch combination band of methanol between 6510 and 6550 cm⁻¹ has been observed for J^′=0-8 and K^′=0-3 at sub-Doppler resolution. In total, 418 lines are assigned and global fits yield molecular torsion-rotation parameters for the upper state. Four K^′-localized perturbations are analyzed and the pattern of residuals is discussed.     

Sub-Doppler and Doppler spectroscopy of DCN isotopomers in the terahertz region: ground and first excited bending states (v1v2v3)=(0 1 0)

The rotational spectra of the deuterium cyanide isotopic species DCN, D¹³CN, DC¹⁵N, and D¹³C¹⁵N were recorded in the vibrational ground and first excited bending state (v₂=1) up to 2 THz. The R-branch transitions from J=3←2 to J=13←12 were measured with sub-Doppler resolution. These very high resolution (∼70 kHz) and precise (±3-10 kHz) saturation dip measurements allowed for resolving the underlying hyperfine structure due to the ¹⁴N nucleus in DCN and D¹³CN for transitions as high as J=10←9. Additional high JR-branch (J=25←24 to J=28←27) transitions around 2 THz and direct l-type (ΔJ=0, J=19 to J=25) transitions from 66 to 118 GHz were recorded in Doppler-limited resolution. For the ground state of D¹³C¹⁵N, the J=1←0 transition was measured for the first time. The transition frequency accuracies for the other deuterated species were significantly improved. These new experimental data, together with the available infrared rovibrational data and previously measured direct l-type transitions, were subjected to a global least squares analysis for each isotopomer. This yielded precise sets of molecular constants for the ground and first excited vibrational states, including the nuclear quadrupole and magnetic spin-rotation coupling constants of the ¹⁴N nucleus for DCN and D¹³CN. The hyperfine structure due to the D, ¹³C, and ¹⁵N nuclei have not been resolved, but led to a broadening of the observed saturation dips.     

希夫碱配合物M3L3(NO3)6(H3O)2的合成与光谱性质

以4-氨基-1,2,4-三氮唑与对二甲氨基苯甲醛为原料, 在冰醋酸催化下合成了配体4-氨基-1,2,4-三氮唑缩对二甲氨基苯甲醛（L）。 然后利用L与过渡金属硝酸盐［M(NO3)2·xH2O(M=Cu,　Co,　Zn,　Cd; x=3～6)］在无水乙醇中反应, 制得固态配合物M3L6(NO3)6(H2O)2。 通过元素分析、 红外光谱、 紫外光谱、 荧光光谱等手段对合成的配体及配合物进行了表征。 实验结果表明, 该物质是一种多晶粉末状的发光材料,　在紫外光的激发下,　在乙醇溶液体系中的荧光发射峰在416 nm处,　为蓝色荧光, 色纯度高,　荧光量子效率高, 而配合物M3L6(NO3)6(H2O)2的荧光发射峰则红移至445 nm左右, 同时荧光强度显著增强。　M3L6(NO3)6(H2O)2中与M(Ⅱ)发生配位作用的基团是配体中三氮唑环上的氮原子。     

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.     

N2-broadening coefficients in the ν3 band of CS2 at room and low temperatures

Using a tunable diode-laser spectrometer, N₂-broadening coefficients have been measured for 15 lines in the ν₃ band of C³²S₂ at room and low temperatures (298, 273.2, 248.2, 223.2, and 198.2 K). These lines with J values ranging from 2 to 62 are located in the spectral range 1519-1545 cm⁻¹. The collisional widths are obtained by fitting each measured spectral line with a Voigt and a Rautian lineshape model and for a few lines we also used a Galatry model. From these results, we have determined the n parameter of the temperature dependence of each broadening coefficient. A semiclassical calculation of these broadenings has been performed by considering in addition to the main electrostatic quadrupole-quadrupole interaction an anisotropic dispersion contribution leading to satisfactory results at all temperatures and providing the n temperature dependence parameter in good agreement with the experimental determination.     

Spectroscopic studies of CO2 trapped in rare gas matrices

Low temperature (5 K) high resolution (0.15 and 0.03 cm⁻¹) absorption spectra of ¹³CO₂ have been recorded in neon, argon, krypton, and xenon matrices, in the ν₃ and ν₂ regions. Diffusion experiments have been performed in krypton and xenon in order to identify vibrational traps which could be responsible for the decrease and shortening of the emission observed after laser excitation: high-frequency structures in the ν₃ region are assigned to dimers and a doubling of the monomer line is due to a site effect. In neon, only a double substitutional site, with a splitting of the degenerate ν₂ vibration, is observed. In argon, as previously reported, a single and a double site are characterized. In krypton and xenon, where ν₂ is not split, only single sites would be predicted. As one of them exhibits a ν₃ line highly sensitive to temperature, we expect a large coupling with the lattice and a fast vibrational relaxation. This site is very likely the vibrational trap we are looking for.     

Infrared and visible spectroscopic studies of the ytterbium doped borate Li6Y(BO3)3

The spectroscopic study of trivalent ytterbium doped Li₆Y(BO₃)₃ is conducted in the UV-visible and infrared range. An excitation in the charge transfer band of ytterbium has been selected in order to reduce the reabsorption effect on the IR emission intensity. The maximum of the emission is located at 972 nm for an excitation at 230 nm. The energy level assignment has been successfully conducted using vibrational spectroscopy to distinguish the pure electronic transitions from the phonon-assisted ones. The splitting of the ²F_5/2 and ²F_7/2 components is equal to 523 cm⁻¹ and 676 cm⁻¹, respectively. The decay time dependence as a function of the concentration is also reported. The calculated value τ_rad is about (1.03 ± 0.01) ms for the 1% doped material. For the highest concentration, an IR excitation gives rise to the observation of a blue-green luminescence caused by two mechanisms: an erbium emission at 550 nm after upconversion and a cooperative luminescence of ytterbium ions.     

Global fit analysis including the ν9 + ν4 − ν4 hot band of ethane: Evidence of an interaction with the ν12 fundamental

The ν₉ fundamental band of ethane occurs in the 12 μm region. It is the strongest band of ethane in a terrestrial window and is commonly used for the identification of ethane in the Jovian planets. The ν₉ + ν₄ − ν₄ band occurs in the same region; neither can be analysed as an isolated band, since both are embedded in the torsional bath of the ground vibrational state. We report here two global fit models including data from both of these bands as well as the ν₃ fundamental and the ν₄, 2ν₄ − ν₄, and 3ν₄ torsional transitions. The first is restricted to −5 ? KΔK ? 15 in the hot band and gives an excellent fit to the included data. Three resonant interactions are identified in this fit—a Coriolis interaction with two resonant cases between the ν₉ torsional stack and that of the ground vibrational state (gs) and a resonant Fermi interaction between the ν₃ fundamental and the gs. Hot band lines with KΔK < −5 are influenced by a fourth perturbation, with a crossing at −11 < KΔK < −10, which has been attributed to an interaction with the ν₁₂ fundamental. A second fit, demonstrating a promising treatment of this interaction, is also presented.     

High-precision frequency measurements of the ν1 + ν3 combination band of C2H2 in the 1.5 μm region

A pair of 1.5 μm semiconductor laser frequency standards have been developed for optical telecommunications use, stabilised to transitions of ¹²C₂H₂ and ¹³C₂H₂, using cavity-enhanced Doppler-free saturation absorption spectroscopy. The absolute frequencies of 41 lines of the ν₁ + ν₃ band of ¹²C₂H₂, covering the spectral region 1520-1545 nm, have been measured by use of a passive optical frequency comb generator, referenced to ¹³C₂H₂ transitions of known frequency. The mean experimental uncertainties (coverage factor k = 1) of the frequency values are 3.0 kHz (type A) and 10 kHz (type B). Improved values of the band origin ν₀, rotational constants B′ and B″, and centrifugal distortion coefficients D′, D″, H′, and H″ are presented.     

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.     

cis Acrolein: Mixing of the S0 and S1 electronic states by the (a″) skeletal torsional vibration

Large effects of vibronic coupling upon vibrational levels of the ground (¹A′) and first excited (¹A″) singlet electronic states of cis acrolein (2-propenal) are successfully modeled. Some implications for CH₂CHCHO spectroscopy and photophysics are discussed briefly.     

Self-broadening coefficients and absolute line intensities in the ν4 + ν5 band of acetylene

Self-broadening coefficients and line strengths have been measured at room temperature for 30 lines of C₂H₂ in the P and R branches of the ν₄ + ν₅ band, using a tunable diode laser spectrometer. These lines, ranging from P(22) to R(23), are located in the spectral range 1275-1390 cm⁻¹. A semiclassical calculation of the line broadenings has been performed considering the main electrostatic interactions and an anisotropic dispersion contribution leading to results in satisfactory agreement with the experimental data.     

The bΣ(b0) → XΣ(X10,X21) and aΔ(a2) → X21 transitions of AsBr

Emission spectra of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺,X₂1) and a¹Δ(a2) → X₂1 transitions of AsBr have been measured in the near-infrared spectral region with a Fourier-transform spectrometer. The arsenic bromide radicals were generated in fast-flow systems by reaction of arsenic vapor (As_x) with bromine and were excited by microwave-discharged oxygen. The most prominent features in the spectrum are the Δv = +1,0,−1, and −2 band sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺) transition in the range 11 700-12 700 cm⁻¹. With lower intensities, the Δv = 0 and −1 sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₂1) sub-system show up in the same range. Further to the red, between 6000 and 6700 cm⁻¹, the Δv = 0, +1, and −1 sequences of the hitherto unknown a¹Δ(a2) → X₂1 transition are observed. Analyses of medium- and high-resolution spectra have yielded improved molecular constants for the X₁0⁺, X₂1, and b0⁺ states and first values of the electronic energy and the vibrational constants of the a2 state.     

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.