Vibration-rotation Parameters Research Articles

Mid-infrared Laser Spectroscopy of Jet-Cooled Formic Acid Trimer: Mode-Dependent Line Broadening in the C-O Stretching Region.

Building on recent progress in the vibrational spectroscopy of the formic acid trimer, we present the first high-resolution measurements of the jet-cooled laser absorption spectrum of (HCOOH)3. The spectra of the lowest- and highest-frequency C-O stretching fundamentals are analyzed whereas the third band is not observed, complicated by monomer and dimer absorptions at 1219 cm-1 (8.2 μm). Vibration-rotation parameters are obtained for the band at 1172.31512(68) cm-1 whereas the C-O stretch at 1246.33(5) cm-1 exhibits a significantly larger breadth, allowing only resolution of the coarse PQR structure. Vibrational predissociation can be ruled out, and intramolecular vibrational redistribution mechanisms are discussed, particularly coupling to the concerted proton exchange within the cyclic dimer subunit. Ultimately, the question remains open. The prospects of high-resolution measurements of other trimer bands or isotope substitution experiments, which might assist in revealing the mode-specificity of the underlying broadening mechanisms, are discussed.

ACCURATE SPECTROSCOPIC CHARACTERIZATION OF OXIRANE: A VALUABLE ROUTE TO ITS IDENTIFICATION IN TITAN'S ATMOSPHERE AND THE ASSIGNMENT OF UNIDENTIFIED INFRARED BANDS.

In an effort to provide an accurate spectroscopic characterization of oxirane, state-of-the-art computational methods and approaches have been employed to determine highly accurate fundamental vibrational frequencies and rotational parameters. Available experimental data were used to assess the reliability of our computations, and an accuracy on average of 10 cm-1 for fundamental transitions as well as overtones and combination bands has been pointed out. Moving to rotational spectroscopy, relative discrepancies of 0.1%, 2%-3%, and 3%-4% were observed for rotational, quartic, and sextic centrifugal-distortion constants, respectively. We are therefore confident that the highly accurate spectroscopic data provided herein can be useful for identification of oxirane in Titan's atmosphere and the assignment of unidentified infrared bands. Since oxirane was already observed in the interstellar medium and some astronomical objects are characterized by very high D/H ratios, we also considered the accurate determination of the spectroscopic parameters for the mono-deuterated species, oxirane-d1. For the latter, an empirical scaling procedure allowed us to improve our computed data and to provide predictions for rotational transitions with a relative accuracy of about 0.02% (i.e., an uncertainty of about 40 MHz for a transition lying at 200 GHz).

Acetylene, 12C 2H 2: Refined analysis of CRDS spectra around 1.52 μm

The analysis of CW-cavity ring down absorption spectra of 12C 2H 2 previously reported by Robert et al. (Mol. Phys. 106 (2008) 2581) was improved in the range 6667–7015 cm −1. Some 1825 lines were newly assigned. They either belong to 105 new sub-bands, involving 69 previously unreported sub-states, or extend assignments in 35 already known sub-bands. A global fit procedure of line positions from the full 12C 2H 2 database containing 18 415 lines, including those newly assigned, was performed, accessing vibrational states up to 8900 cm −1. Coriolis interactions were systematically introduced in the global Hamiltonian, which also accounted for higher order vibrational constants and considered the role of higher excited bending states than before. The dimensionless standard deviation of the fit was 1.07 and 396 effective vibration–rotation parameters were determined. Two local, interpolyad couplings were evidenced for the first time. A set of 121 new lines from 12CH 13CH present in natural abundance in the gas sample were also assigned.

An analysis of a superweak absorption spectrum of the SO2 molecule using the variational procedure

The high resolution structure of a superweak 2ν 1 +ν 2 +ν 3 −ν 2 band of sulfur dioxide, SO 2 , is for the first time recorded with a Bruker IFS-120 HR Fourier spectrometer and analyzed using a specially derived procedure and a relevant computer code. As a result of the analysis, 115 lines have been found in the recorded spectrum, which allowed us to obtain high-accuracy values of the vibrational energy and rotational parameters of the highly excited vibrational state, (211).

Line positions and strengths of 41 bands including 10 OCS isotopologues in the 3850–4200 cm −1 region

The present analysis substantially improves the spectroscopic characterization of near infrared OCS in a window region (3850–4200 cm −1) important for atmospheric studies of Venus. Previous studies in this spectral region cataloged numerous OCS line positions, but accurate line intensities were measured for only three strong bands. In this paper, the corresponding line intensities are obtained for 41 OCS bands, including weak isotopic bands reported for the first time. The 2ν 3 (0002–0000) band is analyzed for 10 OCS isotopologues (adding 16O 13C 34S, 17O 12C 32S, 16O 12C 36S, 18O 12C 34S, and 16O 13C 33S). In addition, observations of 0332–0330 of the main isotope, 16O 12C 32S, provides accurate vibration–rotation parameters for the upper state (and the lower state, 0330 of 16O 12C 32S). Finally, one unidentified band is seen at 3969.3 cm −1; its lower state is clearly the ground state of 16O 12C 32S. The line strengths of these seven previously unanalyzed bands plus 34 other bands of the OCS isotopologues, 16O 12C 32S, 16O 12C 34S, 16O 13C 32S, 16O 12C 33S, and 18O 12C 32S, were least-squares fitted to determine strength parameters, S v and Herman-Wallis coefficients. Finally, the intensities of 17 additional very weak bands were estimated to provide an extensive new database of OCS line parameters to support remote sensing of Venus. The integrated intensity in cm −1/(molecule cm −2) at 296 K is 8.1×10 −19 for the 3800–4200 cm −1 region.

Vibration-rotation pattern in acetylene. II. Introduction of Coriolis coupling in the global model and analysis of emission spectra of hot acetylene around 3 μm

A high temperature source has been developed and coupled to a high resolution Fourier transform spectrometer to record emission spectra of acetylene around 3 mum up to 1455 K under Doppler limited resolution (0.015 cm(-1)). The nu(3)-ground state (GS) and nu(2)+nu(4)+nu(5) (Sigma(u) (+) and Delta(u))-GS bands and 76 related hot bands, counting e and f parities separately, are assigned using semiautomatic methods based on a global model to reproduce all related vibration-rotation states. Significantly higher J-values than previously reported are observed for 40 known substates while 37 new e or f vibrational substates, up to about 6000 cm(-1), are identified and characterized by vibration-rotation parameters. The 3 811 new or improved data resulting from the analysis are merged into the database presented by Robert et al. [Mol. Phys. 106, 2581 (2008)], now including 15 562 lines accessing vibrational states up to 8600 cm(-1). A global model, updated as compared to the one in the previous paper, allows all lines in the database to be simultaneously fitted, successfully. The updates are discussed taking into account, in particular, the systematic inclusion of Coriolis interaction.

Vibration−Rotation Energy Pattern in Acetylene:13CH12CH up to 10 120 cm−1

All 18,219 vibration-rotation absorption lines of (13)CH(12)CH published in the literature, accessing substates up to 9400 cm(-1) and including some newly assigned, were simultaneously fitted to J-dependent Hamiltonian matrices exploiting the well-known vibrational polyad or cluster block-diagonalization, in terms of the pseudo quantum numbers N(s) = v(1) + v(2) + v(3) and N(r) = 5v(1) + 3v(2) + 5v(3) + v(4) + v(5), also accounting for k = l(4) + l(5) parity and e/f symmetry properties. Some 1761 of these lines were excluded from the fit, corresponding either to blended lines, for about 30% of them, or probably to lines perturbed by Coriolis for the remaining ones. The dimensionless standard deviation of the fit is 1.10, and 317 vibration-rotation parameters are determined. These results significantly extend those of a previous report considering levels below only 6750 cm(-1) [Fayt, A.; et al. J. Chem. Phys. 2007, 126, 114303]. Unexpected problems are reported when inserting in the global fit the information available on higher-energy polyads, extending from 9300 to 10 120 cm(-1). They are tentatively interpreted as resulting from a combination of the relative evolution of the two effective bending frequencies and long-range interpolyad low-order anharmonic resonances. The complete database, made of 18,865 vibration-rotation lines accessing levels up to 10 120 cm(-1), is made available as Supporting Information.

Acetylene, 12C2H2: new CRDS data and global vibration-rotation analysis up to 8600 cm−1

The absorption spectrum of 12C2H2 has been recorded using cavity ringdown spectroscopy and analyzed in the ranges 6000 − 6356 cm−1 and 6667−7015 cm−1. Fourteen new bands have been identified and additional J-lines were assigned in 10 already known bands. These new data, together with the published vibration–rotation absorption lines of 12C2H2 accessing vibrational states up to 8600 cm−1 have been gathered in a database. The resulting set includes 12137 transitions involving 186 different k = l 4 + l 5 sub-states, with l i the angular momentum quantum number associated to the i degenerate bending vibration. These lines have been fitted simultaneously to spectroscopic parameters through J-dependent Hamiltonian matrices exploiting the vibrational polyad or cluster block-diagonalization, in terms of the pseudo-quantum numbers Nr = 5v 1 + 3v 2 + 5v 3 +v 4 +v 5 and Ns = v 1 + v 2 + v 3, also accounting for k and e/f parities and u/g symmetry. Modes 1 and 2 correspond to the symmetric CH and CC stretchings, mode 3 to the antisymmetric CH stretch, and modes 4 and 5 to the trans- and cis-degenerate bendings, respectively. The fit was successfully achieved, with a dimensionless standard deviation of 0.92, leading to the determination of 266 effective vibration-rotation parameters.

Measured integrated band intensities and simulated line-by-line spectra for 12C 2HD between 25 and 2.5 μm, and new global vibration–rotation parameters for the bending vibrations

The global analysis of published high-resolution vibration–rotation spectra of 12C 2HD in the bending spectral range is presented, resulting in an extension of the known vibration–rotation assignments, including a new band 2 v 4+ v 5←2 v 4 ( I Π← Δ). Experimental integrated band intensities are reported in the range from 25 to 2.5 μm, and both v 4 and v 5 bending fundamentals are simulated line by line. An extensive line list is produced in the bending energy range, to supply previously missing information in databases.

Vibration-rotation energy pattern in acetylene: C13HC12H up to 6750cm−1

All known vibration-rotation absorption lines of 13CH12CH accessing levels up to 6750 cm-1 were gathered from the literature. They were fitted simultaneously to J-dependent Hamiltonian matrices exploiting the well known vibrational polyad or cluster block diagonalization, in terms of the pseudo-quantum-numbers Ns=v1+v2+v3 and Nr=5v1+3v2+5v3+v4+v5, and accounting also for l parity and ef symmetry properties. The anharmonic interaction coupling terms known to occur from a pure vibrational fit in this acetylene isotopologue [Robert et al., J. Chem. Phys. 123, 174302 (2005)] were included in the model. A total of 12 703 transitions accessing 158 different (v1v2v3v4v5,l4l5) vibrational states was fitted with a dimensionless standard deviation of 0.99, leading to the determination of 216 vibration-rotation parameters. The experimental data included very weak vibration-rotation transitions accessing 18 previously unreported states, some of them forming Q branches with very irregular patterns.

The ν1 and ν4 fundamental bands of H 3Si 37Cl investigated with high resolution

The gas phase infrared spectrum of monoisotopic H 3Si 37Cl has been reinvestigated in the ν 1/ ν 4 region near 2200 cm −1, using a Fourier transform spectrometer, with a nominal resolution of 0.0027 cm −1. The rovibrational analysis confirms, besides the weak Coriolis x, y resonance between the ( v 1 = 1) and ( v 4 = 1) levels, the existence of two strong local perturbations in the ν 4 band. These are caused by rotational (Δ k = Δ l = ±1) type resonances with ν 3 + ν 5 ± 1 + ν 6 ∓ 1 and ν 3 + ν 5 ∓ 1 + ν 6 ∓ 1 , respectively. Another local perturbation of the 12 ⩽ KΔ K ⩽ 14 subbands of the ν 4 band, probably due to a (Δ k = Δ l = ±1) interaction with ν 2 + 2 ν 6 0 , was detected and analyzed. All these local perturbations have been studied individually using a simple model of two interacting sublevels. Without the transitions involved in the local perturbations, more than 2000 lines of the ν 1/ ν 4 band system were used to obtain a complete set of vibration–rotation parameters set for the v 1 = 1 and v 4 = 1 states. By means of a band contour simulation, both the transition moment ratio ∣ M 4: M 1∣ = 1.25 and a positive sign of the Coriolis intensity perturbation were determined. The present results, together with the accurate existing data for ν 2, ν 3, ν 5, and ν 6 bands, allowed us to derive the experimental values, A e = 2.8722945(37) cm −1 and B e = 0.2182248(22) cm −1, which are compared with those of ab initio calculations.

First stretching overtone of BiH3: an extreme local-mode case for XH3-type molecule?

The first stretching overtone region of short-lived, formerly inaccessible BiH3 near 3405 cm(-1) has been measured by Fourier-transform infrared spectroscopy with a resolution of 0.0066 cm(-1). Only the 2nu1(A1)/nu1+nu3(E) band system has been observed. Rotational analysis, with transitions reaching J'max=14, has revealed almost perfect local-mode behavior for the upper states denoted as (200A1/E) in the local-mode notation. Ratios of vibration-rotation interaction parameters q(eff)/alpha(eff)(BB) and r(eff)/alpha(eff)(BC), and the appropriate rotational constant differences, are in good agreement with theoretical local-mode limit values. A simple stretching vibrational model reproduces the observed vibrational term values well, and the potential parameters obtained are close to true values.

Vibrational Spectroscopic Database on Acetylene, X̃ 1Σg+ (12C2H2, C212D2, and C213H2)

Information on the vibrational energy states in acetylene (12C2H2, C212D2, and C213H2) is gathered: spectroscopic constants (vibrational frequencies and anharmonicities, vibration-rotation interaction parameters), observed vibrational energy states and complete sets of predicted vibrational energies and predicted principal rotational constants Bv for states of C212H2, C212D2, and C213H2 up to 15000, 10000, and 12000 cm−1, respectively. Statistical parameters (partition functions and integrated number of states) deduced from these predicted spectroscopic data are provided for the three isotopomers. The equilibrium geometrical structure is determined to be re(CH)=106.138(35) pm and re(CC)=120.292(13) pm from constants available for C212H2, C212D2, C213H2, and C212HD.

Torsional Splitting in the ν5 Fundamental Infrared Band of CH3CD3 and 13CH3CD3

The ν5 fundamental (C–C stretching) of CH3CD3 shows a resolved torsional structure, caused by perturbations due mainly to the linear dependence of the torsional potential barrier on the normal coordinate Q5. We were able to analyze this structure and to assign vibration–rotation transition wavenumbers for all five torsional components, classified according to the symmetry species of the G18(3) extended molecular group. The torsional splitting pattern is qualitatively similar to that of a nondegenerate vibrational state with an even number of excited torsional quanta v6. Explorative calculations show that the main perturber system should consist of the torsional components of the vibrational ground state correlating with v6=4 in the high barrier limit. The strength of the perturbation on the Er0 torsional components of ν5 increases rapidly with r, the E40 component being the most affected. The observed transition wavenumbers can be reasonably fitted by a simplified model containing independent effective vibration–rotation parameters for the five different torsional components of ν5, for both CH3CD3 and 13CH3CD3. The trend of the determined values of the effective vibrational wavenumbers and rotational parameters over the torsional components supports the proposed vibration–torsion interaction mechanism, responsible for the observed torsional splittings. A strong anomaly observed in the rotational intensity distribution of ν5 is discussed.

Mass Derivatives of Molecular Parameters and Distortions in r(2)m Structures

Expressions are derived for the derivatives of various molecular vibration–rotation parameters with respect to atomic masses. These are applied to determine an expression for the mass derivatives of the zero-point moments of inertia, and hence the theoretical substitution coordinates. It is then possible to calculate the distortions in structures determined by means of the r(2)m method. The latter agree well with the distortions found in r(2)m fits of synthetic data.

The Radial Hamiltonians for the X1Σ+ and B1Σ+ States of HCl

All literature vibration–rotational and pure rotational transition energies for the ground X1Σ+ electronic state of H35Cl, H37Cl, D35Cl, and D37Cl, along with the entire collection of electronic B1Σ+ → X1Σ+ emission data for the four isotopomers, have been used in a least-squares fit of compact analytic Born–Oppenheimer potential functions for the B1Σ+ and X1Σ+ electronic states. Additional functions related to the adiabatic and nonadiabatic corrections have also been determined. Separate least-squares fits were made according to the hamiltonian operators of J. K. G. Watson (J. Mol. Spectrosc. 80, 411 (1980)) and R. M. Herman and J. F. Ogilvie (Adv. Chem. Phys. 103, 187 (1998)). The results from the separate analyses demonstrate clearly that the two hamiltonian operators are essentially equivalent, both achieving equally satisfactory representations of the spectral data, and furnishing virtually identical Born–Oppenheimer potential functions. Fully quantum-mechanical vibrational eigenvalues and rotational perturbation series parameters Bv–Ov are presented for the lower levels of the X1Σ+ ground state for which infrared and/or microwave data are available (v" ≤ 7 for H35Cl and H37Cl, v" ≤ 10 for D35Cl and D37Cl). These parameters collectively reproduce the corresponding spectroscopic line positions included in our fit to within the uncertainties of the measurements.

Spectroscopic and ab initio investigation of the νOH overtone excitation in trans-formic acid

Fourier transform spectroscopy and intracavity laser absorption spectroscopy are used to record the absorption spectrum of formic acid at high spectral resolution, in the ranges of the 2νOH (6968.258 cm−1) and 4νOH (13 284.075 cm−1) vibrational bands of the trans-rotamer, respectively. Numerous perturbations combined with a large line density limit the extent to which the vibration–rotation analysis is performed. Some 689 lines are assigned in the first overtone band and related vibration–rotation constants are determined. Only the band origin and upper state principal A-rotational constant are determined for the n=4 overtone band, because of much higher spectral density. Interpolation, helped by literature data, provides all missing principal rotational constants in the nOH series, for n=1 to 4. All major vibration–rotation parameters appear to evolve very smoothly along the series. This trend is fully supported by ab initio calculations performed at the MP2/cc-pVTZ level of theory and based on an effective one-dimensional model describing the OH local mode stretching vibration. Results of these calculations are detailed in terms of the mean nuclear structure in the excitation series, up to n=4. The related calculated dipole moment surface allows the experimental a:b subband intensity ratio in the series to be interpreted in terms of a decrease in the HOC angle, from Θ≈90° (n=1) to 44°(n=4). The potential occurrence of a proton exchange mechanism between the two oxygen nuclei, close to a tautomerism mechanism, is discussed.

Refined Investigation of the Overtone Spectrum of Nitrous Oxide

Following our previous work [A. Campargue, D. Permogorov, M. Bach, M. Abbouti Temsamani, J. Vander Auwera, M. Herman, and M. Fujii, J. Chem. Phys. 103, 5931–5938 (1995)], we reinvestigated the overtone spectrum of nitrous oxide (14N216O) using intracavity laser absorption spectroscopy, observing seven new bands in the spectral range 10 650–12 200 cm−1 and improving the signal-to-noise ratio in two others previously reported using Fourier transform spectroscopy. The earlier FT line positions, in the range 6500–11 000 cm−1, have been calibrated using the 3–0 vibration–rotation line wavenumbers in 12C16O as references. A previously unreported hot band is spotted on the FT spectrum, at 7229 cm−1. Vibration–rotation parameters are provided for all newly analyzed bands and significantly improved for most previously reported FT bands by accounting for more lines in the fitting procedure than earlier. All bands are vibrationally assigned in agreement with theoretical predictions. A table listing all levels above 6500 cm−1 reported in the literature is provided.

Rotational spectrum, ring-puckering vibration and ab initio calculations on 1,1-difluorocyclobutane

The rotational spectra of the ground and first five ring-puckering excited states of 1,1-difluorocyclobutane have been investigated in the centimeter- (8–40 GHz) and millimeter-wave regions (96–106 and 144–159 GHz). Analysis of the spectra for the pairs of coupled vibrational states vp=0/1 and vp=2/3 has been carried out using two-state Hamiltonians, yielding accurate rotational and centrifugal distortion constants, vibration-rotation coupling parameters, and the energy spacings ΔE01 and ΔE23. The spectrum for the vp=4 to vp=6 ring-puckering states was satisfactorily accounted for in terms of effective semi-rigid Hamiltonians for each vibrational state. A double minimum ring-puckering potential function with a barrier to ring inversion of 231(4) cm−1 has been obtained from the analysis of the vibrational dependence of the rotational constants and inversion splittings ΔE01 and ΔE23. The calculated variation of the quartic centrifugal distortion constants with the ring-puckering quantum number reproduces satisfactorily the experimental trends, confirming the validity of the derived potential function. Ab initio calculations with HF, MP2, and B3LYP density functional hybrid methods have been carried out for this molecule using different basis sets. The experimental and ab initio potential functions, coupling terms, and ring-puckering dynamical parameters are compared. Finally, an ab initio near-equilibrium structure is presented.

Millimeter-wave spectroscopy of vibrationally-excited NaCCH [formula omitted] and MgCCH [formula omitted]: the v5 bending mode

Pure rotational spectra of NaCCH ( X ̃ 1 Σ +) and MgCCH ( X ̃ 2 Σ +) have been recorded in their ground state and v 5 vibrational level, the metal–C–C bend, in the range 315–525 GHz using millimeter-wave direct absorption techniques. This data set complements previous measurements. For NaCCH, rotational transitions were recorded for v 5 l =0 0, 1 1, 2 2, 2 0, 3 3, and 4 4 levels, and for the 0 0 states of NaCCD and Na 13 CCH . Transitions originating in the 1 1, 2 0, and 2 2 states of MgCCH were additionally observed. Rotational, l-type doubling, and vibration–rotation parameters have been determined for both species, as well as estimates of the ω 5 bending frequency.