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• Infrared spectra of 2,5-norbornadiene were recorded using a hi-res FTIR. • First rotationally-resolved infrared spectra of six fundamental bands of 2,5-norbornadiene. • Ro-vibrational transitions were assigned and then fit using a semi-rigid rotor Hamiltonian. • This work provides improved ground state spectroscopic constants for the molecule. • Vibrational assignments for 2,5-norbornadiene have been confirmed. Rotationally-resolved infrared absorption spectra of the two lowest-energy fundamental bands for each of the three infrared active symmetry species of 2,5-norbornadiene (C 2 v point group symmetry; asymmetry parameter κ = −0.2203), ν 11 (a 1), ν 12 (a 1), ν 28 (b 1), ν 29 (b 1), ν 38 (b 2), and ν 39 (b 2), have been measured, assigned and fit to a semi-rigid rotor Hamiltonian to produce a set of spectroscopic constants for each band. The fit band centers are ν 11 (a 1), c -type transitions, 728.852357(3) cm−1; ν 12 (a 1), c -type transitions, 417.31604(1) cm−1; ν 28 (b 1), a -type transitions, 656.719741(3) cm−1; ν 29 (b 1), a -type transitions, 500.31425(1) cm−1; ν 38 (b 2), b -type transitions, 800.82243(2) cm−1; and ν 39 (b 2), b -type transitions, 539.23110(6) cm−1. Using ground state combination differences from the ν 11 and ν 28 bands and previously published microwave data, an improved set of ground state spectroscopic constants was fit for the parent isotopologue of the molecule. [ABSTRACT FROM AUTHOR]

Highlights: [•] The PH3 Pentad near 4.5μm is reanalyzed using high resolution FTIR data. [•] Over 4400 line positions and intensities are retrieved from 1950 to 2450cm−1. [•] Positions and intensities are modeled to 0.00133cm−1 and 7.7%, respectively. [•] Splitting in 53 A+A− pairs is observed for K =3,6,9 levels. [•] Nineteen measured self-broadening coefficients of and are compared. [Copyright &y& Elsevier]

Several new infrared absorption bands for 32S16O3 have been measured and analyzed. The principal bands observed were ν1+ν2 (at 1561 cm-1), ν1+ν4 (at 1594 cm-1), ν3+ν4 (at 1918 cm-1), and 3ν3 (at 4136 cm-1). Except for 3ν3, these bands are very complicated because of (a) the Coriolis coupling between ν2 and ν4, (b) the Fermi resonance between ν1 and 2ν4, (c) the Fermi resonance between ν1 and 2ν2, (d) ordinary l-type resonance that couples levels that differ by 2 in both the k and l quantum numbers, and (e) the vibrational l-type resonance between the A1′ and A2′ levels of ν3+ν4. The unraveling of the complex pattern of these bands was facilitated by a systematic approach to the understanding of the various interactions. Fortunately, previous work on the fundamentals permitted good estimates of many constants necessary to begin the assignments and the fit of the measurements. In addition, the use of hot band transitions accompanying the ν3 band was an essential aid in fitting the ν3+ν4 transitions since these could be directly observed for only one of four interacting states. From the hot band analysis we find that the A1′ vibrational level is 3.50 cm-1 above the A2′ level, i.e., r34=1.75236(7) cm-1. In the case of the 3ν3 band, the spectral analysis is straightforward and a weak Δk=±2, Δl3=±2 interaction between the l3=1 and l3=3 substates locates the latter A1′ and A2′ “ghost” states 22.55(4) cm-1 higher than the infrared accessible l3=1 E′ state. [Copyright &y& Elsevier]

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

A Bruker IFS-120HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington was used to record a series of spectra of pure H 2 O and air-broadened H 2 O in the regions of the ν 1 and ν 3 bands (3450–4000 cm −1 ) at different pressures, temperatures and volume mixing ratios of H 2 O in air. Eighteen high-resolution, high signal-to-noise (S/N) ratio absorption spectra were recorded at T = 268, 296 and 353 K using two temperature-controlled absorption cells with path lengths of 9.906(1) and 19.95(1) cm. The resolution of the spectra recorded with the 9.906 cm and 19.95 cm absorption cells was 0.006 and 0.008 cm −1 , respectively. A multispectrum nonlinear least squares fitting technique was employed to fit all the eighteen spectra simultaneously to retrieve 313 accurate line positions, 315 intensities, 229 Lorentz air-broadened half-width and 213 air-shift coefficients and their temperature dependences (136 for air-broadened width and 128 for air-shift coefficients, respectively). Room temperature self-broadened half-width coefficients for 209 transitions and self-shift coefficients for 106 transitions were also measured. Line mixing coefficients were experimentally determined for isolated sets of 10 transition pairs for H 2 O-air and 8 transition pairs for H 2 O-H 2 O using the off-diagonal relaxation matrix element formalism, and 85 quadratic speed dependence parameters were measured. Modified Complex Robert-Bonamy (MCRB) calculations of self-, and air-broadened (from N 2 - and O 2 -broadening) half-width and air-shift coefficients, and temperature dependence exponents of air-broadened half-width coefficients are made. The measurements and calculations are compared with each other and with similar parameters reported in the literature. [ABSTRACT FROM AUTHOR]

A high-throughput CW slit-jet apparatus coupled to a high-resolution FTIR was used to record the asymmetric NO stretch band of nitromethane. The b -type band, including torsionally excited states with m ≤ 3, has been assigned for K a ″ ≤ 10, J″ ≤ 20. The ground state combination differences derived from these assigned levels were fit with the RAM36 program to give an RMS deviation of 0.0006 cm −1 . The band origin is 1583.0 (±0.1) cm −1 and the torsional level spacing is nearly identical to that in the ground state. The upper state levels are split into multiplets by perturbations. A subset of the available upper state combination differences for m = 0, K a ′ ≤ 7, J′ ≤ 10 were fit with the same program, but with rather poorer precision (0.01 cm −1 ) than for the ground state. [ABSTRACT FROM AUTHOR]

Rotational and rovibrational spectra of methyl cyanide were recorded to analyze interactions in low-lying vibrational states and to construct line lists for radio astronomical observations as well as for infrared spectroscopic investigations of planetary atmospheres. The rotational spectra cover large portions of the 36–1627 GHz region. In the infrared (IR), a spectrum was recorded for this study in the region of 2 ν 8 around 717 cm −1 with assignments covering 684–765 cm −1 . Additional spectra in the ν 8 region were used to validate the analysis. Information on the K level structure of CH 3 CN is almost exclusively obtained from IR spectra, as are basics of the J level structure. The large amount and the high accuracy of the rotational data improves knowledge of the J level structure considerably. Moreover, since these data extend to much higher J and K quantum numbers, they allowed us to investigate for the first time in depth local interactions between these states which occur at high K values. In particular, we have detected several interactions between v 8 = 1 and 2. Notably, there is a strong Δ v 8 = ± 1 , Δ K = 0 , Δ l = ± 3 Fermi resonance between v 8 = 1 - 1 and v 8 = 2 + 2 at K = 14 . Pronounced effects in the spectrum are also caused by resonant Δ v 8 = ± 1 , Δ K = ∓ 2 , Δ l = ± 1 interactions between v 8 = 1 and 2 at K = 13 , l = - 1 / K = 11 , l = 0 and at K = 15 , l = + 1 / K = 13 , l = + 2 . An equivalent resonant interaction occurs between K = 14 of the ground vibrational state and K = 12 , l = + 1 of v 8 = 1 for which we present the first detailed account. A preliminary account was given in an earlier study on the ground vibrational state. Similar resonances were found for CH 3 CCH and, more recently, for CH 3 NC, warranting comparison of the results. From data pertaining to v 8 = 2 , we also investigated rotational interactions with v 4 = 1 as well as Δ v 8 = ± 1 , Δ K = 0 , Δ l = ± 3 Fermi interactions between v 8 = 2 and 3. We have derived N 2 - and self-broadening coefficients for the ν 8 , 2 ν 8 - ν 8 , and 2 ν 8 bands from previously determined ν 4 values. Subsequently, we determined transition moments and intensities for the three IR bands. [ABSTRACT FROM AUTHOR]

Accurate knowledge of spectroscopic line parameters of PH3 is important for remote sensing of the outer planets, especially Jupiter and Saturn. In a recent study, line positions and intensities for the Pentad bands of PH3 have been reported from analysis of high-resolution, high signal-to noise room-temperature spectra recorded with two Fourier transform spectrometers (2014) [1]. The results presented in this study were obtained during the analysis of positions and intensities, but here we focus on the measurements of spectral line shapes (e.g. widths, shifts, line mixing) for the 2ν4, ν2 + ν4, ν1 and ν3 bands. A multispectrum nonlinear least squares curve fitting technique employing a non-Voigt line shape to include line mixing and speed dependence of the Lorentz width was employed to fit the spectra simultaneously. The least squares fittings were performed on five room-temperature spectra recorded at various PH3 pressures (~2-50 Torr) with the Bruker IFS-125HR Fourier transform spectrometer (FTS) located at the Pacific Northwest National Laboratory (PNNL), in Richland, Washington. Over 840 Lorentz self-broadened half-width coefficients, 620 self-shift coefficients and 185 speed dependence parameters were measured. Line mixing was detected for transitions in the 2ν4, ν1 and ν3 bands, and their values were quantified for 10 A+A- pairs of transitions via off-diagonal relaxation matrix element formalism. The dependences of the measured half-width coefficients on the J and K rotational quanta of the transitions are discussed. The self-width coefficients for the ν1 and ν3 bands from this study are compared to the self-width coefficients for transitions with the same rotational quanta (J, K) reported for the Dyad (ν2 and ν4) bands. The measurements from present study should be useful for the development of a reliable theoretical modeling of pressure-broadened widths, shifts and line mixing in symmetric top molecules with C3v symmetry in general, and of PH3 in particular. [ABSTRACT FROM AUTHOR]

Abstract: Pure samples of cis,cis- and trans,trans-1,4-difluorobutadiene-2-d 1 have been synthesized, and high-resolution (0.0015cm−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 666cm−1 and one A-type band at 866cm−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 A 0 =0.4195790(4), B 0 =0.0536508(8), and C 0 =0.0475802(9)cm−1. For the trans,trans isomer, three C-type bands at 856, 839, and 709cm−1 have been investigated to give a combined set of 1624 GSCDs. Resulting ground state rotational constants for this isomer are A 0 =0.9390117(8), B 0 =0.0389225(4), and C 0 =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. [Copyright &y& Elsevier]

Abstract: The jet-cooled spectrum of pentafluoroethane (C2HF5) has been recorded between 1100 and 1325cm−1 at a resolution of 0.0022cm−1. A rotational temperature of approximately 10K was achieved by expanding 50Torr of C2HF5 in 500Torr of helium. Transitions belonging to five different fundamental vibrations have been assigned and fit to a Watson Hamiltonian: the ν 3 band at 1309.880494(189)cm−1, ν 4 at 1200.734645(67)cm−1, ν 5 at 1142.78147(33)cm−1, ν 13 at 1223.334098(115)cm−1, and ν 14 at 1147.394185(163)cm−1. The fit of the ν 4 band has an rms deviation of 0.000436cm−1 compared to the uncertainty in the experimental line position of 0.0002cm−1. Satisfactory fits were achieved for the other four bands (ν 3, ν 5, ν 13, ν 14) at this cold temperature, with most of the centrifugal distortion constants fixed at the ground state values. Joint fits with previous work were attempted for the ν 4 and ν 13, successfully in the former case and unsuccessfully in the latter. [Copyright &y& Elsevier]

Abstract: A supersonic free-jet spectrum of the ν 4 band of CF3Cl has been measured using a quantum cascade laser system. Those measurements were combined with a low temperature (−67°C) FTS spectrum of the region 1060–1260cm−1 and with room temperature FTS measurements down to 400cm−1 to give improved values for the rovibrational constants for the ν 1, ν 2, ν 3, 2ν 3, 2ν 5, ν 4, and ν 5 states of CF3 35Cl and CF3 37Cl. The principal perturbation found by earlier investigators in the ν 1 band is treated as a very weak Coriolis interaction at several avoided crossings of the rotational levels of the ν 1 state and the 2ν 5 state with kl <0. None of the other vibrational states showed any signs of perturbations. With these new measurements we now have high resolution data on all of the fundamental vibrational states except ν 6. [Copyright &y& Elsevier]

Abstract: The 2,3-13C2 isotopomer of butadiene was synthesized, and its fundamental vibrational fundamentals were assigned from a study of its infrared and Raman spectra aided with quantum chemical predictions of frequencies, intensities, and Raman depolarization ratios. For two C-type bands in the high-resolution (0.002cm−1) infrared spectrum, the rotational structure was analyzed. These bands are for ν 11 (a u ) at 907.17cm−1 and for ν 12 (a u ) at 523.37cm−1. Ground state and upper state rotational constants were fitted to Watson-type Hamiltonians with a full quartic set of centrifugal distortion constants and two sextic ones. For the ground state, A 0 =1.3545088(7)cm−1, B 0 =0.1469404(1)cm−1, and C 0 =0.1325838(2) cm−1. The small inertial defects of butadiene and two 13C2 isotopomers, as well as for five deuterium isotopomers as previously reported, confirm the planarity of the s-trans rotamer of butadiene. [Copyright &y& Elsevier]

Abstract: Samples of trans,trans and cis,cis forms of butadiene-1,4-d2 have been synthesized and found to contain useful amounts of the cis,trans species as a contaminant. Assignments of fundamental frequencies for the three isotopomers of butadiene-1,4-d2 have been extended and improved from investigations of their Raman spectra as well as their infrared (IR) spectra. High-resolution IR spectra have been recorded for the three isotopomers, and a rotational analysis has been completed for strong bands of each species. Ground state and some upper state rotational constants have been fit. Corresponding ground state moments of inertia compare favorably with equilibrium moments of inertia obtained from B3LYP/6-311++G** theory. Two 13C isotopomers are being prepared, and an improved structural analysis of butadiene will soon be available to assess how π-electron delocalization affects its structure. [Copyright &y& Elsevier]

As part of a series of investigations of isotopic forms of sulfur trioxide, high-resolution infrared and coherent anti-Stokes Raman spectroscopies were used to study the fundamental modes and several hot bands of 32S18O3. Upper levels of hot bands originating from the ν2 and ν4 bending mode states have been found to couple strongly to the upper levels of the IR-inactive ν1 symmetric stretch through indirect Coriolis interactions and Fermi resonances. Coriolis coupling effects are particularly noticeable in 32S18O3 due to the close proximity of the ν2 and ν4 fundamental vibrations, whose deperturbed wavenumber values are 486.48813(4) and 504.28477(4) cm-1. The uncertainties in the last digits are shown in parentheses and are two standard deviations. From the infrared transitions, accurate rovibrational constants are deduced for all of the mixed states, leading to deperturbed values for ν1, α1B, and α1C of 1004.68(2), 0.000713(2), and 0.000348(2) cm-1, respectively. The Be value is found to be 0.310820(2) cm-1, yielding an equilibrium bond length re of 141.7333(4) pm that is, within experimental uncertainty, identical to the value of 141.7339(3) pm reported previously for 34S18O3. With this work, precise and accurate spectroscopic constants have now been determined in a systematic and consistent manner for all the fundamental vibrational modes of the sulfur trioxide D3h isotopomeric forms 32S16O3, 34S16O3, 32S18O3, and 34S18O3. [Copyright &y& Elsevier]

High-resolution (0.0015 cm−1) infrared spectroscopy has been used to study the 34S16O3 IR-active hot bands originating from the ν2 and ν4 bending mode levels and terminating in the states 2ν2 (l=0), ν2+ν4 (l=±1), and 2ν4 (l=0,±2). The upper states are strongly coupled via Fermi resonance and indirect Coriolis interactions to the ν1 symmetric stretching mode levels that are only directly accessible from the ground state via a Raman-active transition. A Coherent anti-Stokes Raman (CARS) spectrum of ν1 for 34S16O3 is presented which is dramatically different from the corresponding one for 32S16O3. From the infrared transitions, accurate rovibrational constants are deduced for all the mixed states, leading to deperturbed values for ν1, α1B, and α1C of 1064.920(84), 0.000 834 5(54), and 0.000 410 (11) cm−1, respectively. The uncertainties in the last digits are shown in parentheses and represent two standard deviations. These parameters reproduce the unresolved Q-branch contour of the CARS spectrum very well. Various other rotational and vibrational parameters have been determined, leading to values of Be=0.349 760 6(33) cm−1 and re=141.734 70(68) pm, values that are identical (within experimental error) to those found for 32S16O3. [Copyright &y& Elsevier]

The infrared spectrum of the ν2,ν4 bending mode region of 34S-substituted sulfur trioxide, 34S16O3, has been recorded at a resolution of 0.0025 cm−1. The ν2 and ν4 levels are coupled by a Coriolis interaction, yielding significant spectral shifts that have been successfully analyzed to obtain rovibrational constants for the ground state and both fundamentals. Comparisons are made with 32S16O3 parameters and the B0 rotational constant is found to be 0.348 556 03(28) cm−1, only very slightly larger than the corresponding value of 0.348 543 33(5) cm−1 for 32S16O3. Coriolis and l-type resonance interactions between the ν2 and ν4 levels produce frequency shifts and strong intensity perturbations in the spectra that are considered for both 34S16O3 and 32S16O3. The resulting analysis yields an average value of ±0.62(8) for the dipole derivative ratio (∂μx/∂Q4x)/(∂μz/∂Q2) and a positive sign for the product of this ratio with the ζy2,4 Coriolis constant, for which experiment gives ±0.5940(15). Ab initio calculations indicate that the signs of ∂μx/∂Q4x and ∂μz/∂Q2 are both positive and hence ζy2,4 is also positive, in agreement with earlier calculations. These signs indicate that the effective charge movement in the xz plane has the same sense of rotation as Q2,Q4x atom motion in this plane that produces a py vibrational angular momentum component, correlated motion that is confirmed by ab initio calculations. [Copyright &y& Elsevier]

Further analysis of the high-resolution (0.0015 cm−1) infrared spectrum of 32S16O3 has led to the assignment of more than 3100 hot band transitions from the ν2 and ν4 levels to the states 2ν2 (l=0), ν2+ν4 (l=±1), and 2ν4 (l=0,±2). These levels are strongly coupled via Fermi resonance and indirect Coriolis interactions to the ν1 levels, which are IR-inaccessible from the ground state. The unraveling of these interactions has allowed the solution of the unusual and complicated structure of the ν1 CARS spectrum. This has been accomplished by locating over 400 hot-band transitions to levels that contain at least 10% ν1 character. The complex CARS spectrum results from a large number of avoided energy-level crossings between these states. Accurate rovibrational constants are deduced for all the mixed states for the first time, leading to deperturbed values of 1064.924(11), 0.000 840 93(64), and 0.000 418 19(58) cm−1 for ν1, α1B, and α1C, respectively. The uncertainties in the last digits are shown in parentheses and represent two standard deviations. In addition, new values for some of the anharmonicity constants have been obtained. Highly accurate values for the equilibrium rotational constants Be and Ce are deduced, yielding independent, nearly identical values for the SO re bond length of 141.734 03(13) and 141.732 54(18) pm, respectively. [Copyright &y& Elsevier]