Search

SF6 and H2 broadening and shift of the vibration–rotation lines in the fundamental band of hydrogen fluoride have been investigated. Using mathematical modeling of measuring the absorption of radiation of an electric discharge HF laser, the possibility of correct calculations of both broadening and shift of HF lines by foreign gases were determined. Measurements for two foreign gases (Ar and N2 for which there are literature data) were made in order to test this approach. The obtained results have been well matched with existing literature data. This allowed us to apply the proposed method for measuring the broadening and shift of the HF lines P(7) and P(8) by SF6 molecules, for which neither the broadening nor the shift of the absorption lines were previously measured, and by H2 molecules, for which only data on the broadening on the overtone band lines are available from the literature. The obtained results were compared with scarce literature data.

We propose a new technique of remote wind measurements based on Doppler analysis of a CO2 absorption line in the 1.605 µm overtone band measured in the direct Sun observation geometry. Heterodyne spectroradiometric measurements of the solar radiation passing through the atmosphere provide an unprecedented spectral resolution up to λ/δλ∼6×107, with a signal-to-noise ratio of more than 100. The shape of the individual rotational line profile provides an unambiguous relationship between the offset from the line center and the altitude at which the respective part of the line profile is formed. Therefore, an inverse problem may be posed in order to retrieve the vertical distribution of wind because with retrievals the vertical resolution is compromised by a spectral resolution and the signal-to-noise ratio of the measurements. A close coincidence between the measured and synthetic absorption line is reached, with retrieved wind profiles between the surface and 50 km being in good agreement with reanalysis models. This method may pose an alternative to widely employed lidar and radar techniques.

We present the first report of optical absorption spectroscopy of H$^{36}\!$Cl, a radioactive isotopologue of hydrogen chloride. We used Fourier-transform infrared spectroscopy to determine the line center wavenumbers of the fundamental rovibrational band lines P(10)-R(10) and the first overtone band lines P(1)-R(7) with total uncertainty of less than 0.0018 cm$^{-1}$ (60 MHz) and 0.007 cm$^{-1}$ (0.2 GHz), respectively, at 68 % confidence level. We also performed a rotational analysis on the bands to determine the related molecular constants. We further compared the linewidths and relative intensities of the lines to those of the stable isotopologues H$^{35}\!$Cl and H$^{37}\!$Cl. The new spectroscopic information assists in developing optical instrumentation for the detection of H$^{36}\!$Cl., Supplementary information can be found at the end of the file (pages 17-24)

IR absorption spectra of mixtures (12CH3) $$_{2}^{{13}}$$ CO/HF and free (12CH3) $$_{2}^{{13}}$$ CO molecules are recorded in the region of 4000−800 cm−1 with a Bruker IFS-125 HR vacuum Fourier spectrometer at room temperature with a resolution of 0.05 cm−1. Absorption bands of the (12CH3) $$_{2}^{{13}}$$ CO…HF complex are obtained by subtracting the absorption bands of free HF and acetone molecules and absorption lines of atmospheric water from the experimental spectrum of mixtures. Spectral characteristics of the 2ν(13C=O) overtone band of free acetone were also recorded. Comparison of the spectral data obtained with the analogous data measured earlier for the (12CH3) $$_{2}^{{12}}$$ CO…HF complex shows changes in the absorption spectra of complexes caused by 12C → 13C isotopic substitution. The frequencies and intensities for absorption bands of both complexes are calculated using the perturbation theory and methods MP2/6-311++G(2d,2p) and MP2/6-311++G(3df,3pd) with allowance for the error of superposition of basis functions of the monomers. The calculated results are in good agreement with the experimental data and are used to interpret the observed spectra. The influence of anharmonic effects on the frequencies and intensities of the strongest ν(H–F) and ν(13C=O) bands is examined with the help of variational calculations. It is shown that, unlike the (12CH3) $$_{2}^{{12}}$$ CO…HF complex, the 2ν(13C=O)/ν(H–F) resonance is virtually absent in the (12CH3) $$_{2}^{{13}}$$ CO…HF complex.

High-resolution, mid-infrared spectra of methanol isotopologues (CH3OH, CH3OD, CD3OH, and CD3OD) embedded in superfluid helium nanodroplets have been obtained. For the normal isotopologue, we observed the CO stretching overtone band, the lines within which are 2× broader than in the fundamental for E species methanol and no different than the fundamental for A species methanol. For CH3OD, we observed the CO stretching overtone band for the first time, which was characterized by narrow line widths for both nuclear spin species. Spectra in the CD3 stretching bands were much broader, which is attributed to rapid relaxation to nearby anharmonically coupled vibrational state(s). Apparently the coupling is much stronger for CD3OD, for which the rotational substructure is completely washed out. Inertial analyses of the rotationally resolved fundamental and overtone bands reveal that the moment of inertia of helium, ΔIHe, that couples to rotation decreases in going from the heavier (CD3OH) to lighter (CH3OH) isot...

Optical-optical double-resonance spectroscopy with a continuous wave pump and frequency comb probe allows measurement of sub-Doppler transitions to highly excited molecular states over a wide spectral range with high frequency accuracy. We report on assessment and characterization of sub-Doppler double-resonance transitions in methane measured using a 3.3-$\ensuremath{\mu}\mathrm{m}$ continuous wave optical parametric oscillator as a pump and a 1.67-$\ensuremath{\mu}\mathrm{m}$ frequency comb as a probe. The comb spectra were recorded using a Fourier transform spectrometer with comb-mode-limited resolution. With the pump tuned to nine different transitions in the ${\ensuremath{\nu}}_{3}$ fundamental band, we detected 36 ladder-type transitions to the $3{\ensuremath{\nu}}_{3}$ overtone band region, and 18 V-type transitions to the $2{\ensuremath{\nu}}_{3}$ overtone band. We describe in detail the experimental approach and the pump stabilization scheme, which currently limits the frequency accuracy of the measurement. We present the data analysis procedure used to extract the frequencies and intensities of the probe transitions for parallel and perpendicular relative pump-probe polarization. We compare the center frequencies and relative intensities of the ladder-type transitions to theoretical predictions from the TheoReTS and ExoMol line lists, demonstrating good agreement with TheoReTS.

International audience; The room temperature spectrum of the very weak third overtone band of carbon monoxide in natural isotopic abundance is recorded by cavity ring down spectroscopy (CRDS) referenced to a frequency comb, between 8206 and 8465 cm-1. The sensitivity of the recordings (noise equivalent absorption on the order of min~ 5×10-12 cm-1) allowed for measuring lines with intensity as weak as 1×10-30 cm/molecule at a recording pressure limited to 10.0 Torr. The use of low pressure values (1.0 and 10.0 Torr) helped to minimize the impact of profile effects on the derived line positions and line intensities. The line profile analysis was performed using the speed dependent Nelkin-Ghatak model for the 10 Torr recordings while the Voigt profile was found sufficient to account for the line shapes recorded at 1.0 Torr. Overall, line parameters of 227 transitions are derived. The observed transitions belong to the 4-0 band of the 12C16O, 13C16O, 12C18O and 12C17O isotopologues present in natural abundance in the sample and to the 5-1 hot band of 12C16O. For a large part of the observations, line positions are reported with accuracy as good as 4×10-6 cm-1 (~120 kHz). The selfinduced line shift of the 4-0 band is reported for the first time from the position values at 1 and 10 Torr. Using literature values of the 1-0, 2-0 and 3-0 bands, the vibrational dependence of the self-induced pressure shift in CO is discussed. The experimental values of the 12C16O v= 4 energy levels J < 26 are reproduced with a standard deviation of 2.5×10-6 cm-1 (75 kHz). The intensities of the 12C16O lines reported with an accuracy better than 1% show an overall good agreement with literature values in particular with those included in the HITRAN database.

In this work a new method to calculate anharmonic vibrational ground and excited state energies is proposed. The method relies on the auto-adjusting perturbation theory (APT) which has been successfully used to diagonalize square matrices. We use as zeroth order correction the self-consistent vibrational energies, and with the APT approach we calculate the vibrational anharmonic correlation correction to any desired order. In this paper we present the methodology and apply it to a model system and formaldehyde. Vibrational APT approach shows a robust convergent behavior even for the states where the standard (Rayleigh-Schr¨odinger) vibrational Møller-Plesset perturbation theory is clearly divergent E.B. and J.M.B. thank the project CTQ2006-04410/BQU of the Spanish Ministerio de Ciencia y Tecnología. O.C. acknowledges support from the Danish Center for Scientific Computing (DCSC), the Danish national research foundation, the Lundbeck Foundation, and EUROHORCs for a EURYI award. J.M.L thanks the project CTQ2008-06696/BQU of the Spanish Ministerio de Ciencia y Tecnología

Infrared absorption spectra of CO in the region of the first overtone have been observed in dilute (approximately 1 to 10 parts in 1000) liquid solutions of oxygen, nitrogen, and argon, and clear crystalline nitrogen and argon matrices. The overtone band was found at 4249.0, 4252.4, and 4252.0 cm-1 with half widths of 18.4, 17.8, and 13.7 cm-1 in liquid oxygen, nitrogen, and argon solutions at 82, 78, and 82 °K, respectively. The half width in liquid oxygen varied from 18.4 to 10.0 cm-1 in the temperature range 82 to 57 °K. The band position was the same but its width was smaller in the crystalline nitrogen matrix. Two bands were observed in the clear crystalline argon solid at 4245 and 4256 cm-1. The solution results cannot be interpreted with the recent theory of Buckingham.

Near-infrared absorption spectra obtained for aqueous solutions of eight aprotic organic compounds at concentrations up to 10% molar fraction were analyzed in detail using principal component analysis to determine the variation in the hydrogen-bonded network of water upon dissolution of the compounds. The shape of the overtone band of the O–H stretching mode, which is a sensitive indicator of the condition of the hydrogen-bonded network, was observed to vary with concentration and temperature. Principal component analyses revealed that all observed spectral variations consisted mainly of two components. The first component was similar to that observed for pure water upon a temperature change. The second component contributed to an increase in absorption intensity in the lower frequency region upon dissolution of any organic compound. This observation supports a model that involves the dissolution of an aprotic compound that generates ice-like aggregates of water molecules in the solution. In contrast, the contribution of the first component depends on the type of solute and its concentration; the first component contributes either to strengthening of the hydrogen-bonded network (similar to the change upon a temperature decrease) or to weaken it (similar to the change upon a temperature increase).

A low-resolution (0.5 cm−1) Fourier transform infrared (FTIR) spectrum of formaldehyde-d2 (D212CO) in the 2500–4500 cm−1 region was recorded to study the combination bands in this region. The bands ν 2 + ν 4 , ν 2 + ν 6 , ν 2 + ν 3 , ν 1 + ν 2 , ν 2 + ν 5 , 3 ν 3 , 2 ν 2 and 2 ν 5 were identified and their band centers (with an uncertainty of ± 0.1 cm−1) and band types were determined. Furthermore, the high-resolution FTIR spectrum of the 2 ν 2 overtone band (3315–3440 cm−1) of D212CO was recorded at an unapodized resolution of 0.0063 cm−1 and its infrared lines were analyzed. A total of 970 rovibrational transitions have been assigned and fitted up to J′ = 35 and Ka′ = 14 using the Watson’s A-reduced Hamiltonian in the Ir representation. Upper state ( v 2 = 2) rovibrational constants inclusive of three rotational and five quartic centrifugal distortion constants were accurately determined for the first time. The band center of the 2 ν 2 band was determined as 3385.200666 ± 0.000035 cm−1. The rms deviation of the rovibrational fit was 0.00093 cm−1. From the fitting of 451 ground state combination differences (GSCDs) of D212CO which were derived from the infrared transitions of the 2 ν 2 band of this work, together with 360 microwave frequencies from a previous study, new and accurate ground state constants of D212CO up to three octic terms were obtained. The combination and overtone bands and the newly assigned high-resolution infrared lines of the 2 ν 2 band in the 2500–4500 cm−1 region can be used to detect D212CO in this infrared region. In addition, the results derived from this study give information on the rovibrational molecular structure of D212CO.

Anharmonic vibrational state calculations were performed for PtCO and Ar-PtCO via the direct vibrational configuration interaction (VCI) method based on CCSD(T) energies and CCSD dipole moments at tens of thousands of grids, to get insights into the anomalous effect of a solid argon matrix on the vibrational spectra of PtCO. It was shown that, through the binding of Ar to PtCO via a strong van der Waals interaction, the Pt-C-O bending fundamental level drastically loses the infrared intensity although the corresponding overtone band shows a relatively large intensity. The origin of this phenomenon was analyzed based on the dipole moment surfaces and electron densities around the equilibrium structure. The present computations have solved the inconsistency between the gas-phase and the matrix-isolation experiments for PtCO.

Frequency-stabilized cavity ring-down spectroscopy was used to determine helium-broadened 12C16O line shape parameters for eleven lines in the 3 → 0 vibrational overtone band, including helium pressure broadening and pressure shifting. The spectra provided evidence of two non-Voigt mechanisms affecting line shape: collisional (Dicke) narrowing and speed dependence of the line broadening. Multispectrum fits of the speed dependent Nelkin-Ghatak profile (with the quadratic approximation for speed dependence) enabled precise determinations of the line shape parameters associated with these two mechanisms. The measured line shape parameters are presented and are compared to past work for helium-broadened 12C16O transitions in the 3 → 0 vibrational band (broadening coefficients) and in the 1 → 0 fundamental vibrational band (broadening and shifting coefficients). Significant reductions in the uncertainty of the broadening coefficients are demonstrated, along with the first determinations of helium pressure shifting and narrowing parameters for this transition. Analysis of the spectra at elevated pressure reveals evidence of line mixing with fitted first-order line mixing parameters that are consistent with literature values.

International audience; We present experimental data on the line pressure broadening and shift coefficients in the first vibrational overtone band of HCl in mixtures with CO and CO2 gas at room temperature. CO-broadening coefficients are published for the first time. The CO2-broadening coefficients and shifts for both systems are in very good agreement with the literature data and have better accuracy than earlier results. Collisions with CO2 lead to stronger broadening for the most lines than collisions with CO. Similar to the broadening coefficients, the absolute values of CO2-induced shift coefficients are larger than those for HCl-CO system. However, the asymmetric shifts are very similar for both systems except for R2(0) and P2(1) lines, where the interaction anisotropy has the strongest influence.

The second bending overtone band 3ν2 of sulfur dioxide has been studied for the first time with high resolution rotation-vibration spectroscopy. The 1530 transitions involving 728 upper state energy levels with Jmax.= 53 and K a m a x . = 15 have been assigned to the 3ν2 band. The 746 transitions belonging to the 3 ν 2 − ν 2 “hot” band have been also assigned in the region of 950–1100 cm − 1 . For the analysis of the assigned transitions, an effective Hamiltonian of an isolated (030) vibrational state (the Watson operator in A-reduction and Ir representation) was used. Set of 9 varied parameters was determined which reproduce the initial experimental data with the drms deviations of 9.0 × 10 − 4 cm − 1 and 9.8 × 10 − 4 cm − 1 for the 3ν2 and 3 ν 2 − ν 2 bands, which are comparable with the experimental uncertainties.

Transitions of the 6ν3 overtone band of 14N216O near 775 nm have been studied by continuous-wave cavity ring-down spectroscopy. Line positions and intensities were derived from a fit of the line shape using a hard-collisional profile. The line positions determined with absolute accuracy of 5×10−4 cm−1 allowed us to reveal finer ro-vibrational couplings taking place after J>14 except a strong anharmonic interaction identified by the effective Hamiltonian model. The absolute line intensities have also been retrieved with an estimated accuracy of 2% for a majority of the unblended lines. A new set of ro-vibrational and dipole moment parameters were derived from the experimental values. A comparison between the line positions and intensities of the 6ν3 band obtained in this work and those from previous studies is given.

Fast decay of both the reactant and product states is shown to strongly increase the intrinsic electron transfer rate in donor–acceptor dyads. The decay is associated with redistribution/relaxation of excited vibrational states that typically participate in the reaction. Although the role of the reorganization of high-frequency vibrational modes in electron-transfer dynamics is well understood and it is commonly accepted to strongly affect the ultrafast electron transfer dynamics, the influence of the relaxation of excited vibrational states on electron transfer is not accounted for in experimental data analysis. In photoinduced electron transfer, excited states of high-frequency vibrational modes are often produced by laser pump pulse so that the ultrafast charge separation, at least partly, occurs from excited vibrational states. The charge recombination accompanying the charge separation also essentially occurs from excited vibrational states of intermediates to form a final excited vibrational state. ...

International audience; We present experimental results on pressure broadening and shift coefficients in the first vibrational overtone band of HCl in gaseous mixtures with H2 and CH4 at room temperature. The whole set of collisional parameters for HCl-CH4 is novel. Most of the data for HCl-H2 system is also published for the first time. Our results have a precision of about 2% or better for shifts and below 1% for broadening in the band center.

We report observations of the high (R$\sim$18000) and medium (R$\sim$5900) resolution, near-infrared spectra of Jupiter's polar regions with the GNIRS instrument at the Gemini North telescope. The observations correspond to the area of main auroral oval in the South and the main spot of the Io footprint in the North. We detected and assigned 18 emission lines of the H$_{3}^{+}$, 2$\nu_{2}\rightarrow 0$ overtone band in the region from 4800 to 4980 cm$^{-1}$ and 5 additional lines in the extended low-resolution spectrum. We use our new modelling scheme, ATMOF to remove telluric absorption bands of CO$_2$ that feature strongly in the 2 $\mu$m region. The H${_2}$ 1-0 S(1), S(2) and S(3) emission lines are also detected in the observed spectral region. We found the rotational temperature and column density of H$_{3}^{+}$ emission at the peak intensity for both northern and southern auroral regions to be the same within the measurement errors (T$_{rot} \sim950$K and N(H$_{3}^{+}$) $\sim$ 4.5$\times10^{16}$m$^{-2}$). The estimates of T$_{rot}$ from H$_{2}$ are consistent within much higher uncertainties with temperatures derived from H$_{3}^{+}$ emissions. We derived the profiles of the H$_{3}^{+}$ emissivity and ion density for both auroral regions providing the first such measurement for the emission associated with the main spot of the Io footprint. We also found a number of weaker lines in the high-resolution spectra that could be associated with emission from high excitation levels in neutral iron, which could be deposited in Jupiter's atmosphere as a result of meteor ablation., Comment: Accepted for publication in Icarus

To determine high-precision values of rotational-vibrational levels of the ground state of the 13C12CH4 molecule, high-resolution spectra in the infrared range 600–1700 cm–1 and microwave transitions known from the literature are used. The rotational and centrifugal parameters of the ground vibrational state with root-mean- square deviation that is by about thousand times smaller than for the parameters known from the literature are determined based on the obtained information.

High-resolution absorption spectrum of the rotational-vibrational 2ν3 band of the S18O2 molecule has been registered for the first time. An analysis of the band by the method of combination differences allows rotational-vibrational structure of the (v = 2, A 1) state to be determined. The inverse spectroscopic problem is solved based on the data obtained.

In this paper, we study vibrational relaxation of CO molecules with excited electronic states. We consider three electronic terms and account for VV exchanges of vibrational energy within each electronic term, VT transitions of vibrational energy into a translational one, and VE exchange of vibrational energy between electronic terms. The initial vibrational state of the gas is strongly nonequilibrium. The effect of VE exchange on the vibrational relaxation of CO molecules is estimated for different kinds of initial vibrational distributions, in particular, the Treanor and Gordiets ones generalized for gases with electronically excited states. The set of equations of state-to-state vibrational kinetics, together with the gas dynamic equations, is solved numerically in the zero-order approximation of the Chapman–Enskog method for the case of spatially homogeneous relaxation. The following results are obtained: neglecting VE exchanges leads to an incorrect assessment of the number density for each electronic level; however, the error is small for the ground electronic state. It is shown that VE exchanges qualitatively affect the time dependence of the vibrational temperature.

Unraveling vibrational coupling is the key to consistently interpret vibrational spectra of complex molecular systems. The vibrational spectrum of the water surface heavily suffers from vibrational coupling, which hinders complete understanding of the molecular structure and dynamics of the water surface. Here we apply heterodyne-detected sum frequency generation spectroscopy to the water surface and accomplish the assignment of a weak vibrational band located at the lower energy side of the free OH stretch. We find that this band is due to a combination mode of the hydrogen-bonded OH stretch and a low-frequency intermolecular vibration, and this combination band appears in the surface vibrational spectrum through anharmonic vibrational coupling that takes place exclusively at the topmost surface.

A systematic study of the dependences of information inequalities relating the variance, Fisher information, and Shannon entropy power in the coordinate and momentum spaces (the Cramer–Rao, Stam, Bialynicki–Birula–Mycielsky–Beckner, and other inequalities) on the vibrational quantum number of a diatomic molecule is performed for the first time. These dependences are calculated for the ground electronic state of the 7Li2 molecule using the semiempirical data available in the literature on the many-parameter potential curve of this state. Specific features of these dependences have been analyzed, their essentially nonmonotonic behavior was revealed, and not only quantitative, but also qualitative, distinctions between these dependences were observed. These results were compared with the results of our calculation in the classical mechanics approximation, and significant (up to a factor of 3.5) discrepancies between these data were observed not only for low-lying, but also for highly excited vibrational levels that are close to the dissociation limit. The results obtained can be used in quantum informatics, analysis of an intramolecular structure and the interaction processes involving the vibrational states of diatomic molecules.

In the present work we report a combined experimental and theoretical study on the molecular structure and vibrational spectra of m-chlorosulfinylaniline. The substance was characterized by 1H and 13C NMR and GC-mass spectrometry as well as by FT-IR and Raman spectroscopy. Experimental results were complemented with theoretical calculations at the B3LYP and MP2 levels of theory for electronic structure and harmonic oscillator and Vibrational Self-consistent Field levels of theory for vibrational structure. The observed and calculated frequencies were found to be in good agreement. Natural Bond Orbital analysis provides an explanation of the stability of the molecule and its electronic properties upon charge delocalization. Fil: Chemes, Doly María. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia; Argentina Fil: Alonso de Armiño, Diego Javier. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia; Argentina Fil: Robles, Norma Lis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina Fil: Cutin, Edgardo Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina

International audience; Classical molecular dynamics simulations (CMDS) are used for calculations of the collision-induced absorption (CIA) by pure N2 in the (2.1-2.2 µm) region of the first overtone band. They lead to reasonable (±15%) agreement with the only two laboratory measurements available, at 97 K and room temperature. Based on these experiment/theory comparisons, empirical corrections are made to the CMDS-calculated CIA of pure N2 in the 200-300 K temperature range. In addition, the contribution of N2-O2 collisions is, in the absence of any laboratory measurement, calculated and a simple semiempirical model (the first of its kind) is built in order to predict the CIA of N2 under Earth atmosphere conditions. This is successfully validated by comparisons with ground-based atmospheric transmission spectra in the 2.1-2.2 µm region.

Coherent nuclear wave packet motions in an electronic excited state of a molecule are measured directly by time-resolved spontaneous fluorescence spectroscopy with an unprecedented time resolution by using two-photon absorption excitation and fluorescence upconversion by noncollinear sum frequency generation. With an estimated time resolution of approximately 25 fs, wave packet motions of vibrational modes up to 1600 cm-1 are recorded for coumarin 153 in ethanol. Two-color transient absorption at 13 fs time resolution are measured to confirm the result. Vibrational displacements between the ground and excited states and Huang-Rhys factors (HRFs) are calculated by quantum mechanical methods and are compared with the experimental results. HRFs calculated by density functional theory (DFT) and time-dependent DFT reproduce the experiment adequately. This fluorescence-based method provides a unique and direct way to obtain the vibrational spectrum of a molecule in an electronic excited state and the HRFs, as well as the dynamics of excited states, and it might provide information on the structure of an excited state through the HRFs.

High resolution spectrum of the trans-C2H2D2 molecule is analyzed on the basis of the Ground State Combination Difference method in the region 1450–1650 cm–1, in which the hybrid ν7 + ν8 band is located. The analysis is performed in the framework of the model which takes into account the Coriolis interaction with the ν8 + ν10 band. The b-type transitions that in their turn, allow more experimental data on the ν7 + ν8 band to be obtained, are determined for this band for the first time.

We present a closed-form expression of the classical vibrational partition function for the improved Rosen-Morse potential energy model. We give explicit expressions for the vibrational mean energy, vibrational specific heat, vibrational free energy, and vibrational entropy for diatomic molecule systems. The properties of these thermodynamic functions for the Na2 dimer are discussed in detail. We find that the improved Rosen-Morse potential model is superior to the harmonic oscillator in calculating the heat capacity for the Na2 molecules.

We report a comparison of the analysis of the low energy spectrum of 13CHF3 and 12CHF3 from the THz (FIR) range to the ν1 fundamental at high resolution (δ[small nu, Greek, tilde] < 0.001 cm-1 or otherwise Doppler limited) on the basis of FTIR spectra taken both with ordinary light sources and with the synchrotron radiation from the Swiss Light Source. Several vibrational levels are accurately determined including, in particular, the 2ν4 CH-bending overtone and the ν1 CH-stretching fundamental of 13CHF3. Comparison of experimental results with those from accurate full dimensional vibrational calculations allows for a study of the time-dependent quantum dynamics of intramolecular vibrational redistribution (IVR) in the CH chromophore both on short time scales (fs) and longer time scales (ps) when coupling to the lower frequency modes becomes important and where the 12C/13C isotope effects are very large.

Collisional quenching of NO A(2)Σ(+) (v = 0, 1) by O2 has been studied through the detection of vibrationally excited products by time-resolved Fourier transform infrared emission spectroscopy. Non-reactive quenching of NO A(2)Σ(+) (v = 0) produces a vibrational distribution in NO X(2)Π which has been quantified for v = 2-22, and is found to be bimodal. The results are consistent with two quenching channels. The first forms the ground X(3)Σ or low-lying a (1)Δg electronic state of O2 with a distribution including high vibrational levels of NO X(2)Π which is slightly hotter than statistical. Two possibilities are identified for the second channel. The first, with a similar quantum yield to that producing higher vibrational levels, forms a highly electronically excited state, such as O2 c(1)Σ, with low vibrational levels in NO X(2)Π which are inverted with a distribution resembling that resulting from a sudden or harpoon mechanism. The second is that ground state oxygen is formed with low vibrational energy partitioned into NO X(2)Π. In addition, vibrationally excited NO2 is observed, but at intensities which indicate that it is formed in low quantum yield. Quantitatively unobservable processes (defined as those which do not form ground state NO (v ≥ 2)) are found to have a branching ratio of at most 25 ± 5%. The results are compared with those of previous studies and the most consistent interpretation suggests that dissociation of O2 to form ground state O((3)P) atoms and ground vibrational state NO X(2)Π (v = 0) is the main reactive process rather than NO2 formation. Qualitatively similar results are seen for the quenching of NO A(2)Σ(+) (v = 1).

We propose a substantially simplified approach to construct a pair of 2D asynchronous spectra based on the DAOSD approach proposed in our previous papers. By using a new concentration series, only three 1D spectra are used to generate a pair of 2D correlation spectra together with two reference spectra. By using this method, the previous problem of labor intensive traditional DAOSD approach has been successfully addressed. We apply the new approach to characterize intermolecular interaction between acetonitrile and butanone dissolved in carbon tetrachloride. The existence of intermolecular interaction between the two solutes can be confirmed by the presence of a cross peak in the resultant 2D IR spectra. In addition, the absence of cross peak around (2254, 2292) in Psi(butanone) provides another experimental evidence to reveal the intrinsic relationship between the stretching band and an overtone band (delta(CH3)+v(C-C)). (C) 2016 Elsevier B.V. All rights reserved.

A ppb-level CO sensor based on multi-comb optical-feedback cavity enhanced absorption spectroscopy with a 2.3 μm diode laser was developed for SF6 decomposition analysis in electric power system. The effective optical path reached to 4.5 km within 35 cm length cavity. Besides, through modulating the cavity length five times automatically, the spectral resolution was improved to 0.0015 cm−1 from 0.0071 cm−1. Targeting the R(6) line of CO first overtone band at 4285.01 cm−1, which is interference free from absorption spectra of SF6 mixtures (SF6, SO2, H2S, SO2F2, HF, CF4, CO2, COS, O2 and H2O), the minimum detection limit and detection precision under different gas pressures were performed. At optimum integration time of 30 s determined by Allan deviation analysis and gas pressure of 40 torr, the minimum detection limit and detection precision of CO were better than 18 ppb and 150 ppt, respectively.

Shock tube experiments are carried out to study the physical and chemical processes during a vehicle entry into the Mars atmosphere using tunable diode laser absorption spectroscopy (TDLAS) and optical emission spectroscopy (OES). CO concentration distributions are diagnosed behind a shock wave in a CO2-N2 mixture with three different conditions of initial pressure and velocity. The strong shock wave is established in a shock tube driven by combustion of hydrogen and oxygen. Time-resolved spectra of the Δv = 0 sequence of the B2Σ+ →X2Σ+ electronic transition of CN have been observed through OES. A precise analysis of the CN violet spectra is performed and used to determine rotational and vibrational temperatures. Two absorption lines in the first overtone band of CO near 2.33 μm, are selected from a HITRAN simulation to calibrate laser wavelength and detect the CO concentration. Combined with these temperature results using OES, CO concentrations in the thermal equilibrium region are derived, which are 2.91 × 1017 cm-3, 7.46 × 1017 cm-3 and 1.01 × 1018 cm-3, corresponding to equilibrium temperatures equal to 7000 ± 400 K, 7400 ± 300 K, 6000 ± 300 K in the low, medium and high pressure conditions, respectively.

We present here new medium resolution spectra ($\lambda/\Delta\lambda$ $\sim$ 1200) of K$-$M giants covering wavelength range 1.50$-$1.80 and 1.95$-$2.45 $\mu$m. The sample includes 72 K0$-$M8 giants from our TIRSPEC observations and all available 35 giants in that spectral range from archival IRTF spectral library. We have calibrated here the empirical relations between fundamental parameters (e.g., effective temperature, surface gravity) and equivalent widths of some important spectral features like Si I, Na I, Ca I, $^{12}$CO. We find that the $^{12}$CO first overtone band at 2.29 $\mu$m and second overtone band at 1.62 $\mu$m are a reasonably good indicator of temperature above 3400 K and surface gravity. We show that the dispersion of empirical relations between $^{12}$CO and $T_{eff}$ significantly improve considering the effect of surface gravity., Comment: 17 pages, 10 figures, Accepted for publication in MNRAS

A ppm-level CO sensor based on a 2f wavelength modulation spectroscopy (2f-WMS) technique was developed for the application of SF6 decomposition analysis in an electric power system. A detailed investigation of the optimum target line selection was carried out to avoid spectral interference from high purity SF6 in a wide wavelength range. A diode laser emitting at 2.33 μm and a 14.5-m multipass gas cell (MGC) was employed to target the R(6) line of the CO first overtone band and increase the optical path, respectively, thus resulting in a minimum detection sensitivity of 1 ppm. A Levenberg-Marquardt nonlinear least-squares fit algorithm makes full use of the information from all data points of the 2f spectrum and as a result, a measurement precision of ~40 ppb was achieved with a data update rate of 0.6 s. The sensor performance was also evaluated in terms of the gas flow rate, stability, and linearity. The results showed that the best operating condition with a precision of 6 ppb can be achieved by increasing the gas flow rate to the value that matches the optimum averaging time of 48 s.

Rovibrational spectra of Ar–N2O and nonpolar (N2O)2 van der Waals complexes have been recorded from 1157.2 to 1176.7 cm−1 in 2v2 overtone band region of N2O monomer using an external-cavity quantum cascade laser to probe the direct absorption in a slit supersonic jet expansion. One a/b hybrid vibrational band was identified for nonpolar (N2O)2, and one b-type vibrational band for Ar–N2O, respectively. Quantum chemical calculations of vibrational frequencies and infrared intensities of these two complexes were performed at the MP2/aug-cc-pvtz level of theory. The first vibrational band is assigned tentatively as a combination band of the intramolecular symmetric and anti-symmetric in-plane bending modes of nonpolar (N2O)2. The second vibrational band is assigned as an overtone band of the bending mode of Ar–N2O. Precise molecular constants have been derived for these two complexes. The band-origin is located at υ 0 = 1168.177584(76) cm−1 for Ar–N2O and υ 0 = 1165.218580(54) cm−1 for nonpolar (N2O)2, which shows a blue-shift by 0.0451 cm−1 for Ar-N2O and a red-shift by 2.9139 cm−1 for nonpolar (N2O)2 compared with that of the N2O (0200)-(0000) band, respectively.

The equilibrium geometry, the binding energy, and harmonic and anharmonic spectral parameters of H2CO and HF monomers and the H2CO∙∙∙HF complex are calculated in the MP2/6-311++G(3df,3pd) approximation with the basis set superposition error taken into account. Anharmonic calculations are carried out using the second-order vibrational perturbation theory. The changes in transition frequencies and intensities of monomeric IR bands upon formation of the 1:1 complex are analyzed. A high intensity value (53 km mol–1) is predicted for the overtone band of the out-of-plane HF libration. The variational method was used to solve anharmonic vibrational problems in 1D–4D subspaces involving the H–F stretch. The influence of anharmonicity on spectral and structural parameters was studied. The variational calculation confirmed the high intensity value for the overtone of the HF librational mode from the perturbative calculation. Matrix-isolation experiments were performed in N2 at T = 8 K to record the absorption spectra of pure H2CO and HF and H2CO/HF mixtures in the IR region. The spectral features related to the H–F, C=O, and C–H stretches and the in-plane HF librational motion were reliably identified. The predictions of our perturbative calculations for isolated compounds, especially for the band shifts upon complexation, are in satisfactory agreement with the experimental matrix-isolation findings. The only exception is the H–F stretching mode in the complex because of the high anharmonicity of HF and strong interaction of free HF molecules with a matrix environment. Of particular interest is the observation of a rather strong band at 1069 cm–1, which is close to 1072 cm–1 predicted for the overtone of HF out-of-plane librational mode.

The chemical analysis of carbonaceous and organic materials in geological samples (i.e., rocks) is an important and necessary step of hydrocarbon resource development. Despite some significant advances in the last several decades, there still is a need for improved analytical techniques that deliver greater sensitivity and reliable information regarding source rock properties and characterisation. Infrared spectroscopy is a promising technique in terms of providing both qualitative and quantitative information on carbonaceous materials. However, the application of this method for routinely determining parameters relevant to the organic geochemistry of geological systems has not been widely accepted. Here, we compare infrared spectroscopy to standard methods for deriving the total organic carbon content, number of free/volatile hydrocarbons and the hydrocarbon generating potential in shale rocks. Two common methods for collecting infrared spectra, namely Attenuated Total Reflectance (ATR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, were evaluated to determine which one is most suitable for shale characterisation. It was revealed that the carbonate overtone band is largely responsible for causing quantitative interferences and errors. Although DRIFT was more sensitive, it was found that the ATR method is less prone to spectral interferences caused by the carbonate overtone band. Irrespective, both methods yielded reasonable correlations against established analytical techniques providing that the C H absorption band was corrected for variations in the carbonate content.