Search

Spectra of 99% isotopically pure 15NH3 were recorded using cavity ring-down (CRD, 6567−6639 cm−1) and Fourier transform (FT, 6350–6985 cm−1) spectroscopy under jet cooled and room temperature conditions, respectively. Measured line positions on both data sets improve on literature values, in particular by one order of magnitude for the ν1+ν3 band. A room temperature list of line positions, with approximate line intensities, is provided, much more complete and precise than presently available. Line broadening effects in the CRD spectrum allowed lines with J′′′- values between 0 and 3 to be identified. Ground state combination differences were used to refine the assignments, further assisted by intensity ratios between the two data sets. Reliable values for J, K and inversion symmetry of the ground state vibrational levels, as well as further information on a/s doublets could be obtained, updating and extending literature assignments.

The high-resolution infrared spectrum of deuterated acetylene containing one C-13 atom, (CCD2)-C-13-C-12, has been recorded by Fourier transform spectroscopy in the range 450-1700cm(-1). The upsilon(4) and upsilon(5) bending fundamental bands and a number of overtone, combination and hot bands were identified. In total, 3210 rotation vibration transitions were assigned to 27 bands involving bending states with both upsilon(4) + upsilon(5) and |l(4) + l(5)| up to 3. The ground state and 13 vibrationally excited states were characterised, i.e., all the l-vibrational components of the excited bending manifolds with upsilon(4) + upsilon(5) up to 2, ((II)pi), ((II)pi), and (pi and phi). Two simultaneous least-squares fits of all assigned transitions have been performed, one considering transitions with upsilon(4) + upsilon(5) up to 2, the other adding the transitions with upsilon(4) + upsilon(5) = 3. The model Hamiltonian adopted for the analysis takes into account the usual vibration and rotation l-type resonances within each vibrational manifold and the Darling-Dennison anharmonic resonance between and , and between and . Two sets of 33 and 42, respectively, spectroscopic parameters were derived. They reproduce 1512 and 2450 assigned transitions with root mean square values of 3.5 x 10(-4) and 3.9 x 10(-4) cm(-1), respectively. The transitions of four hot bands reaching the ((II)pi) state were fitted simultaneously to the effective upper state parameters.

The infrared spectrum of a sample containing C-13 mono-substituted isotopologues of acetylene, (HCCH)-C-12-C-13, (HCCD)-C-12-C-13, (DCCH)-C-12-C-13 and (DCCD)-C-12-C-13 has been recorded in the 6130-6800cm(- 1) region using a femto-Fourier transform-cavity enhanced absorption spectroscopy (femto-FT-CEAS) apparatus. Three bands for both (HCCD)-C-12-C-13 and (DCCH)-C-12-C-13 were observed and analysed, namely 2(1) - GS and associated hot bands from (4) and (5). The assignment of the 2(1) overtone already reported in the literature [J.L. Hardwick, Z.T. Martin, M.J. Pilkenton, E.N. Wolf, J. Mol. Spectrosc. 243, 10 (2007)] was considerably extended to higher J values. For the (DCCD)-C-12-C-13 isotopologue, four bands were analysed, (1) + (2) + (3) - GS and associated hot bands from (4) and (5) and 2(1) + (4) + (5) - GS

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.

15NH3 is the object of extensive investigation due to the central role of ammonia in astronomical sciences and to the complexity of modeling its interacting vibrationally excited states. Of major interest in astrochemistry is the determination of the 14N/15N ratio in space, characterized by unexpected variability among different solar system objects and reservoirs. Recently, the spectroscopic analysis of ground and v2 = 1 a, s states of 15NH3 has been completed at experimental accuracy. Here, the characterization of the a, s inversion symmetry levels of v2 = 1, 2 and v4 = 1 states is presented. New spectra of 15NH3 have been recorded from 325 to 2000 cm−1 at a resolution ranging from 0.00096 cm−1 to 0.003 cm−1, using the Canadian Light Source synchrotron at CLS. 7518 transitions covering nine bands, ν2, 2ν2, ν4, 2ν2 ← ν2, ν4 ← ν2, 2ν2 ↔ ν4 and the inversion-rotation transitions in the excited states, have been fitted simultaneously. The effective Hamiltonian adopted includes all symmetry allowed interactions between and within the studied excited states, according to the most recent results on ammonia. The transitions have been reproduced at experimental accuracy using 185 spectroscopic parameters, determined with high precision. The leading diagonal parameters, Gv, B, C, D’s, compare well with those of 14NH3. The wavenumbers of the assigned transitions are compared with their theoretically predicted values. An improved set of ground state parameters is also derived. These results noticeably improve the wavenumber line list in the high-resolution transmission molecular absorption (HITRAN) database.

The high resolution infrared spectrum of 123SbD3 has been recorded in the 20–350 cm−1 range and in the regions of the ν1, ν3 and ν2, ν4 fundamental bands centred at 1350 and 600 cm−1, respectively. Splitting of the K′′ = 3, 6 lines have been observed both in the rotation and ro-vibration spectra. A large number of ‘perturbation allowed‘ transitions with selection rules Δ(k −l) = ± 3, ± 6, and ± 9 have been identified in all fundamental bands. Accurate ground state molecular parameters have been determined by means of a simultaneous fit of the rotational transitions and about 12 000 ground state combination differences from the infrared bands. The A and B reductions of the rotational Hamiltonian provided almost equivalent results. The molecular parameters of the ν i = 1 (i = 1 − 4) states were obtained as a result of the simultaneous analysis of the ν1 (A1)/ν3 (E) stretching and of the ν2 (A1)/ν4 (E) bending dyads. In fact, the corresponding excited states are affected by strong perturbations due to rovi...

We report on the observation of the Π (1 1 ; 2NH) ← Σ (0 0 ; ground state) band in 15 NH 3 –Ar, with origin at 6615.943 cm −1 , using jet-cooled cw-cavity ring-down spectroscopy. The rotational temperature is estimated to be 7 K. Nineteen rotational lines were assigned. Perturbations were evidenced from anomalous line positions and line widths, but not unraveled. Upper state rotational constants were obtained from the analysis of the nine unperturbed R / P lines. The e -symmetry upper state predissociation lifetimes appear to decrease with J ′, from about 1.2 ns to 250 ps from J ′ = 1 to 9.

Two new bands. 2nu(1) + nu(2) + nu(3) + 2nu(5) and 5nu(3) with origin at 12220.692 and 12496.158 cm(-1), respectively, were identified on new FT-ICLAS spectra of (C2HD)-C-12 and rotationally analyzed. The rotational analysis of two known bands, with origin at 12038.538 and 12234.872 cm(-1) was extended. Another band, 2nu(1) + 2nu(5) with origin at 7843.6622 cm(-1), was identified for the first time and rotationally analyzed, from a high pressure conventional FT spectrum. Some 115 known vibrational state energies in the molecule, extending up to the visible range.. were used to produce updated vibrational constants. Both a straightforward Dunham model and a global model accounting for a single anharmonic resonance, K-1/255, were used. The results are discussed. (C) 2004 Elsevier Inc. All rights reserved.

Jet-cooled spectra of 14NH3 and 15NH3 in natural abundance were recorded using cavity ring-down (CRDS, 6584–6670 cm−1) and cavity enhanced absorption (CEAS, 6530–6700 cm−1) spectroscopy. Line broadening effects in the CRDS spectrum allowed lines with J ″-values between 0 and 3 to be identified. Intensity ratios in 14NH3 between the jet-cooled CRDS and literature room-temperature data from Sung et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1066) further assisted the line assignments. Ground state combination differences were extensively used to support the assignments, providing reliable values for J, K and inversion symmetry of the ground state vibrational levels. CEAS data helped in this respect for the lowest J lines, some of which are saturated in the CRDS spectrum. Further information on a/s doublets arose from the observed spectral structures. Thirty-two transitions of 14NH3 were assigned in this way and a limited but significant number (19) of changes in the assignments results, compared to Sung et al. or to Cacciani et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1084). Sixteen known and 25 new low-J transitions were identified for 15NH3 in the CRDS spectrum but the much scarcer literature information did not allow for any more refined assignment. The present line position measurements improve on literature values published for 15NH3 and on some line positions for 14NH3.

4 p.: gráf., We report the first experimental observation of homonuclear propensity in collisional relaxation of a polyatomic molecule. A pump-probe stimulated Raman setup is used to pump population to a single rotational level of the v2 = 1 vibrationally excited state in 13C12CD2 and then monitor the redistribution of the rotational population that has taken place after a fixed delay. The Q-branch of the 2ν2–ν2 band shows a pattern of intensity alternation between the even and the odd rotational components, with the greater intensities always corresponding to the rotational levels with the same parity as the one where all the population was initially deposited. The effect can be explained by the existence of a propensity rule that favors collisional relaxation between rovibrational levels of the same parity. © 2011 American Institute of Physics., Funding received from the Spanish Ministry of Science and Innovation through research Grant No. FIS2009-08069; support from CONSOLIDER-INGENIO 2010 Program CSD2009-00038

Infrared and Raman spectra of dideuterated acetylene containing one 13C atom, 13C12CD2, have been recorded and analysed to obtain detailed information on the fundamental 2 band and associated combination and hot bands. Infrared spectra were recorded at 4103cm1 resolution in the region 11502900cm1, which contains combination and hot bands from the ground and the bending v4¼1 and v5¼1 states. The Q-branches of the 2 fundamental and associated hot bands (2þ44, 2þ55, 2þ2424, 2þ2525 and 2þ4þ5(4þ5)) were recorded using inverse Raman spectroscopy, with an instrumental resolution of about 3103cm1. In addition, the observation of the 222 Raman band was carried out populating the v2¼1 state by stimulated Raman pumping. In total, 11 Raman and 9 infrared bands were analysed, involving all the l-vibrational components of the excited stretchingbending manifolds up to vt¼v4þv5¼2. A simultaneous analysis of all infrared and Raman assigned transitions has been performed on the basis of a theoretical model which takes into account the rotation and vibration l-type resonances within each vibrational manifold and the DarlingDennison anharmonic resonance between the 2þ24 and 2þ25 states. The parameters obtained reproduce the assigned transition wavenumbers with a standard deviation of the same order of magnitude as the experimental uncertainty.

The high-resolution infrared spectrum of two partially deuterated isotopologues of acetylene, (HCCD)-C-12-C-13 and (HCCD)-C-13-C-12, has been recorded by Fourier transform spectroscopy in the range 450-1850 cm(-1). The bending fundamental bands and a number of overtone, combination and hot bands have been identified for both isotopomers. In total, 17 vibrational bands for (HCCD)-C-12-C-13 and 18 bands for (HCCD)-C-13-C-12 were analyzed, involving all the I-vibrational components of the excited bending states up to v(t)= v(4) + v(5) = 2. The data pertaining to each molecule were analyzed together with the pure rotational transitions recorded in the millimeter- and sub-millimeter-wave frequency ranges and the v(5)

The Raman spectra of the Q branches of the hot bands associated with the ν2 stretching fundamental of 13 C 2 D 2 (ν 2 +ν 4 –ν 4 , ν 2 +ν 5 –ν 5 , ν 2 +2ν 4 –2ν 4 , ν 2 +2ν 5 –2ν 5 , ν 2 +ν 4 +ν 5 –(ν 4 +ν 5 )) have been recorded using inverse Raman spectroscopy with an instrumental resolution of about 3×10 −3 cm −1 . A simultaneous analysis of all the assigned transitions has been performed on the basis of a theoretical model which takes into account the rotational and vibrational l-type resonances within each vibrational manifold and the Darling–Dennison anharmonic resonance between the ν2+2ν4 and ν2+2ν5 states. The determined parameters reproduce the assigned wavenumbers with a standard deviation of the same order of magnitude as the experimental uncertainty.

International audience; The infrared spectrum of 12C2HD has been studied using synchrotron radiation at the far-infrared beamline, Canadian Light Source, Saskatoon, Canada. The spectra were recorded at a resolution of 0.00096 cm-1 in the 60 to 360 cm-1 range using a Bruker IFS125 Fourier transform spectrometer. Altogether, 821 vibration rotation lines were observed and assigned to P(J), Q(J) and R(J) transitions of the ν5 ← ν4 difference band and associated hot bands with J" up to 35 and (ν4 + ν5) up to 3. These new transitions were analyzed together with 4518 transitions involving bending states with (ν4 + ν5) up to 3 available in the literature. The spectroscopic parameters obtained from the fit reproduce 4909 transitions with a standard deviation of 0.00028 cm-1. The ν5 ← ν4 bands of the 13CH12CD and 12CH13CD molecules were also detected and analyzed.

The infrared spectrum of stibine, SbH 3 , has been recorded in the regions between 720 and 1000 cm -1 and between 1750 and 2020 cm -1 at a resolution of about 0.004 cm -1 . Rovibrational transitions belonging to the ν 2 , ν 4 bending and ν 1 , ν 3 stretching fundamental bands have been measured and assigned for both 121 Sb and 123 Sb isotopomers. Strong perturbations due to rovibrational interactions have been observed both in the bending and in the stretching bands. Splittings of the K ″=3, 6, and 9 lines have been observed and perturbation-allowed transitions with selection rules Δ ( k −l)=±3, ± ±6, and ±9 have been also identified. Simultaneous analyses of transitions belonging to the ν 2 /ν 4 or ν 1 /ν 3 dyads have been performed. The central frequencies of the hyperfine structures of the rotational transitions in the v 2 =1 and v 4 =1 states, recorded in the microwave region by Fourier transform spectroscopy [H. Harder, C. Gerke, and L. Fusina, J. Chem. Phys. 114, 3508–3523 (2001)], have been included in the data set. The theoretical model adopted explicitly takes into account the Coriolis interactions between the v 1 =1 (A 1 ) and v 3 =1 (E) and between the v 2 =1 (A 1 ) and v 4 =1 (E) states, including also several essential resonances within them.

The stretching fundamental bands of the isotopically substituted acetylene 13C2D2 have been recorded and analysed. The Raman spectra of the Q branch of v 1 and v 2, Σ+ g -Σ+ g bands, have been recorded with an instrumental resolution of about 3.0 x 10−3 cm−1 using inverse Raman spectroscopy. The infrared spectrum has been recorded in the region between 2350 cm−1 and 2500 cm−1 with an instrumental resolution of 4.0 x 10−3 cm−1. Transitions belonging to the v 3, Σ+ u -Σ+ g , fundamental band have been identified and assigned. The vibrational energies and the rotational and centrifugal distortion constants of the excited states of all the observed transitions have been determined. The molecular parameters obtained reproduce the assigned wave-numbers with a standard deviation of the same order of magnitude as the experimental uncertainty.

The vibration–rotation spectra of 13C monosubstituted acetylene, 12C13CH2, have been recorded in the region between 450 and 3200 cm−1 with an effective resolution ranging from 0.004 to 0.006 cm−1. A total of about 5300 rovibrational transitions have been assigned to 53 bands involving the bending states up to vt=v4+v5=4, allowing the characterization of the ground state and of 30 vibrationally excited states. All the bands involving states up to vt=3 have been analyzed simultaneously by adopting a model Hamiltonian which takes into account the vibration and rotation l-type resonances. The derived spectroscopic parameters reproduce the transition wavenumbers with a RMS value of the order of the experimental uncertainty. Using the same model larger discrepancies between observed and calculated values have been obtained for transitions involving states with vt=4. These could be satisfactorily reproduced by only adopting, in addition to the previously determined parameters which were constrained in the analysis, a set of effective constants for each vibrational manifold.

The Raman spectra of the Q branch of the ν2 band of 12C2D2 and associated hot bands (ν2+ν4−ν4, ν2+ν5−ν5, ν2+2ν4−2ν4, ν2+2ν5−2ν5, ν2+ν4+ν5−(ν4+ν5), and 2ν2−ν2) have been recorded with an instrumental resolution of about 3×10−3 cm−1 and analyzed. All of them have been recorded using high resolution inverse Raman spectroscopy. For 2ν2−ν2, this technique has been combined with stimulated Raman pumping in order to populate the υ2=1 state. A simultaneous analysis of all the observed Raman transitions and of the ν2−ν5 band recorded in the infrared region has been performed on the basis of a theoretical model which takes into account the rotational and vibrational l -type resonances within each vibrational manifold and the Darling–Dennison anharmonic resonance between the ν2+2ν4 and ν2+2ν5 states. The determined parameters reproduce the assigned wavenumbers with a standard deviation of the same order of magnitude as the experimental uncertainty.

International audience; The absorption spectrum of 12C2H2 has been recorded using cavity ring downringdown spectroscopy and analyzed in the ranges 60006356 cm and 66677015 cm. 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 have been gathered in a database. The resulting set includes 12137 transitions involving 186 different k = l4 + l5 sub-states, with li 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 = 5v1+3v2+5v3+v4+v5 and Ns = v1+v2+v3, 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.

Infrared absorption cross-section and integrated absorption intensities of HFC-125 (pentafluoroethane) and HFC-143a (1,1,1-trifluoroethane) vapour have been calculated from their infrared spectra in the region 500–1400 and 700–1500 cm−1 for HCF-125 and HCF-143a, respectively. Spectra have been recorded by means of a Fourier transform spectrometer at a maximum resolution of 0.03 cm−1 at six temperatures in the range 203–293 K on the pure vapour and air mixtures at total pressures of 50, 200 and 800 hPa. A comparison between results obtained in this work and all the data reported previously in the literature has been reported.

An intercomparison of measurements of infra-red absorption cross-sections and integrated absorption intensities in HCFC-22 has been carried out. Independent measurements were made by five spectroscopy groups so that their experimental methods and data reduction techniques could be critically examined. The initial results showed a spread in reported values for integrated absorption intensity over the mid infra-red spectral region that were larger than the reported uncertainties. Re-examination of experimental and data reduction methods resulted in consistency of results within the reported errors. It was found that particular attention had to be paid to controlling and characterising errors associated with the non-linear response of MCT detectors and pre-amplifiers, adsorption of the sample on surfaces in the absorption cell, effectiveness of mixing when making measurements on mixtures of absorber gas and a buffer gas, and location of the photometric “full-scale” and “zero” levels.

The IR absorption spectrum of phosphine (PH3) has been recorded at a resolution of 0.004 cm−1 in the region between 750 and 1400 cm−1. About 2500 rovibrational transitions have been measured and assigned to the ν2 (A1) and ν4 (E) bending fundamentals, including 501 “perturbation allowed” transitions with selection rules Δ(k−l)=±3, ±6, and ±9. Splittings of the K″=3, 6, and 9 lines were observed. Rotational transitions in the vibrationally excited states have also been identified in the far-IR spectra recorded in the past at 0.002 cm−1 resolution between 30 and 200 cm−1 [L. Fusina and M. Carlotti, J. Mol. Spectrosc., 130 (1988) 371]. The rotational structure in the ν2=1 and ν4=1 vibrational states up to J=K=24 was reproduced by fitting simultaneously our experimental data, together with the very accurate transitions previously reported in the literature. The adopted rovibrational Hamiltonian explicitly took into account the Coriolis interaction between the ν2=1 and ν4=1 states, and included also several essential resonances within them. The 46 parameters obtained from the fit reproduced 2736 IR and far-IR transitions retained in the final cycle within the uncertainty of the experimental measurements and 37 microwave and mm-wave transitions with an rms value of 0.9 MHz. The ground state parameters have also been improved by means of ground state combination differences.

International audience; A total of 3155 vibration-rotation line positions providing accurate information on all known vibration-rotation states up to 3000 cm-1 in 12C2H2 were gathered from the literature. Additional 966 lines were assigned on new spectra. The full data set was simultaneously fitted using an appropriate Hamiltonian, with 85 refined parameters. A dimensionless standard deviation equal to 0.86, accounting for 92 % of the lines, was achieved. The vibrational transition dipole moment of the v5 = 1 ← v4 = 1 band observed in the far-infrared was estimated to be │μ5←4│ = 0.55 D with 20 % accuracy, from absolute intensity measurements for a few Q-branch lines.

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.

A total of 134 vibrational levels with assigned rotational structure have been gathered in the ground electronic state of 13C2H2. Most of these measurements are updated or new compared to the previously published data. Altogether, they cover the range up to 23 670 cm−1. 118 out of the 119 levels observed below 13 000 cm−1 have been simultaneously fitted using the so-called cluster model, already used to deal with the vibrational energy levels in other isotopomers of acetylene [El Idrissi et al., J. Chem. Phys. 110, 2074 (1999), and references therein]. Twenty-nine vibrational constants have been determined, including the off-diagonal parameters K3/245, K1/244, K1/255, K11/33, K14/35, and r45, with a rms of the fit equal to 0.52 cm−1. The same three constants of the motion as in 12C2H2 emerged, Ns=v1+v2+v3, Nr=5v1+3v2+5v3+v4+v5 and k=l4+l5. The energies of the levels above 13 000 cm−1 calculated with the obtained parameters compare reasonably well with the experimental values. For all levels the predicted ...

The Raman spectra of the Q branches of the ν1+ν2−ν2 band of 12C2H2 and of the ν1+ν2−ν2 and 2ν2+2ν5−ν2 bands of 13C2H2 were recorded at high resolution in the gaseous phase. To obtain the spectra a two-step pump/probe technique was used. In the first step, molecules were pumped from the ground to the v2=1 excited state by means of a double pulsed stimulated Raman process. Then, spectra corresponding to the transitions from this state to higher ones are recorded by means of a high resolution quasicontinuous stimulated Raman process. The analysis of the experimental data, taking into account the fourth-order anharmonic interaction coupling the excited states for the 13C isotopomer, provided unperturbed values for the rotational and distortion constants of the excited states and for the band origins. Accurate values for the x120 anharmonicity constant have been calculated directly from the energies of the v1=v2=1 states for the first time.

Infrared absorbance cross sections and integrated band strengths for benzene pure vapour have been determined at 273, 298, and 323 K in the region between 600 and 1900 cm−1 by Fourier Transform spectroscopy. This region includes the relevant atmospheric window between 700 and 1200 cm−1. Air broadened spectra of benzene vapour have also been recorded at room temperature (298 K), using mixtures containing 20 kPa and 80 kPa of dry air. Spectra were recorded in the region of the ν4 band (600–800 cm−1) at a resolution of 0.03 and 1.0 cm−1 for the pure vapour and at a resolution of 0.05 cm−1 for the benzene/air mixture, and in the region 900–1900 cm−1 at a resolution of 0.1 cm−1 for both pure benzene and air containing mixtures.

The high resolution infrared spectrum of 121SbD3, recorded between 20 and 350 cm−1 and in the regions of bending and stretching fundamental bands, centred at 600 and 1350 cm−1, has been analysed. Splittings of the K″=3, 6 lines have been observed both in the rotation and ro-vibration spectra. A large number of ‘perturbation allowed‘ transitions with selection rules Δ ( k − l ) = ± 3 , ±6 and ±9 have been identified in all fundamental bands. Accurate ground state molecular parameters have been determined fitting simultaneously the rotational transitions and about 9000 ground state combination differences obtained from lines assigned in the ro-vibrational spectra. The A and B reductions of the rotational Hamiltonian have been applied in the analysis of the ground state. They provided almost equivalent results. The molecular parameters of the 11, 21, 31 and 41 states have been obtained from the simultaneous analysis of the ν1 (A1)/ν3 (E) stretching and of the ν2 (A1)/ν4 (E) bending dyads. In fact, the corresponding excited states are affected by strong perturbations due to Coriolis and k-type rovibrational interactions that have been treated explicitly in the model adopted for the analysis. Improved effective ground state and equilibrium geometries have been determined and compared to those of 121SbH3 and of 123SbD3. Ab initio calculations at the coupled cluster CCSD(T) level with an energy-consistent large-core pseudopotential and large basis sets have been carried out to determine the equilibrium structure, the anharmonic force field, and the associated spectroscopic constants of 121-stibine. The theoretical constants and structural parameters are in good agreement with the experimental data.

The rotation spectrum of stibine; SbH3, in the ground vibrational state was recorded in the region between 30 and 100 cm(-1) at an unapodized resolution of about 0.0015 cm(-1). Delta J = +1, Delta K = 0 transitions were measured and assigned up to J" = 15 and K = 12 for both Sb-121 arid Sb-123 isotopomers. The data of each molecule were analyzed together with the J=0, 1 rotational transitions reported in the literature, a few A(1)-A(2), K = 3 :splitting transitions and K = 1

We have performed the rovibrational analysis of the absorption spectrum of 12C2D2 between 5150 and 8000 cm−1, recorded by Fourier transform absorption spectroscopy, and between 12 800 and 16 600 cm−1, recorded by intracavity laser absorption spectroscopy. Respectively 10 and 9 bands are reported for the first time in each range. Improved or new rovibrational parameters were obtained for 34 vibrational levels altogether. The vibrational energies we obtained, together with those reported in the literature, were taken into account to model the vibrational energy pattern in 12C2D2(X 1Σg+). The analysis was performed in successive steps, inferring each time suitable parameters. The 44/55, 11/33, 12/33, and 1/244 quartic order anharmonic resonances were introduced during the procedure. They altogether define vibrational clusters which are characterized by only two dynamical constants of motion, Ns=V1+V2+V3 and k=l4+l5.

The high-resolution infrared spectrum of deuterated acetylene containing one 13C atom, 13C12CD2, has been recorded by Fourier transform spectroscopy in the range 450–1700 cm−1. The υ4 and υ5 bending fundamental bands and a number of overtone, combination and hot bands were identified. In total, 3210 rotation vibration transitions were assigned to 27 bands involving bending states with both υ4 + υ5 and |l4 + l5| up to 3. The ground state and 13 vibrationally excited states were characterised, i.e., all the l-vibrational components of the excited bending manifolds with υ4 + υ5 up to 2, (IIΠ), (IIΠ), and (Π and Φ). Two simultaneous least-squares fits of all assigned transitions have been performed, one considering transitions with υ4 + υ5 up to 2, the other adding the transitions with υ4 + υ5 = 3. The model Hamiltonian adopted for the analysis takes into account the usual vibration and rotation l-type resonances within each vibrational manifold and the Darling−Dennison anharmonic resonance between and , and between and . Two sets of 33 and 42, respectively, spectroscopic parameters were derived. They reproduce 1512 and 2450 assigned transitions with root mean square values of 3.5 × 10−4 and 3.9 × 10−4 cm−1, respectively. The transitions of four hot bands reaching the (IIΠ) state were fitted simultaneously to the effective upper state parameters.

Fourier-transform intracavity laser absorption spectroscopy allowed five 12 C 13 CH 2 Σ + –Σ + bands, all from the ground state, to be identified in the 0.83 μm range. Their rotational analysis was performed and rotational constants are provided. Three of these bands, with origins at 11616.9684(18), 11737.2356(14), and 11761.0322(23) cm −1 , have never been reported before. Their upper states are assigned to v 1 v 2 v 3 v 4 l 4 v 5 l 5 = 1302 0 2 0 , 1301 1 3 - 1 , and 2201 1 1 - 1 , respectively.

The cubic and quartic force fields of HOCl are investigated on the basis of the most recent experimental data on vibration-rotation interaction constants and anharmonicity constants. Some discrepancies with respect to previously reported ab initio results are found and discussed. The geometrical parameters of this molecule are also evaluated from recent data on the equilibrium values of the moments of inertia.© 1996 Published by Elsevier B.V., Cooperation Program between CNR of Italy and CSIC of Spain. Spanish DGICYT, project PB93-0138.

The submillimeter-wave spectrum of H2O2 has been recorded by means of a tunable FIR spectrometer. Stark measurements have been performed on three selected transitions in the n = 0 state, namely, the 2(20)-1(10) (tau = 4

High resolution vibration-rotation spectra of 13C2H2 were recorded in a number of regions from 2000 to 5200 cm−1 at Doppler or pressure limited resolution. In these spectral ranges cold and hot bands involving the bending-stretching combination levels have been analyzed up to high J values. Anharmonic quartic resonances for the combination levels ν1 + mν4 + nν5, ν2 + mν4 + (n + 2) ν5 and ν3 + (m − 1) ν4 + (n + 1) ν5 have been studied, and the l-type resonances within each polyad have been explicitly taken into account in the analysis of the data. The least-squares refinement provides deperturbed values for band origins and rotational constants, obtained by fitting rotation lines only up to J ≈ 20 with root mean square errors of ≈ 0.0003 cm−1. The band origins allowed us to determine a number of the anharmonicity constants xij0.

Absorption spectra of C2H2 have been recorded between 50 and 1450 cm−1, with a resolution always better than 0.005 cm−1, using two different Fourier transform spectrometers. Analysis of the data provided two sets of results. First, the bending levels with Σt Vt(t = 4, 5) ≤ 2 were characterized by a coherent set of 34 parameters derived from the simultaneous analysis of 15 bands, performed using a matrix Hamiltonian. The following main parameters were obtained (in cm−1): ω40 = 608.985196(14), ω50 = 729.157564(10); B0 = 1.17664632(18), α4 = −1.353535(86) × 10−3, α5 = −2.232075(40) × 10−3; q40 = 5.24858(12) × 10−3, and q50 = 4.66044(12) × 10−3, with the errors (1σ) on the last quoted digit. Second, a more complete set of bending levels with Σt Vt ≤ 4, some of which have never previously been reported, and also including V2 = 1 have been fitted to 80 parameters. This simultaneous fit involved 43 bands and used the same full Hamiltonian matrix. Some perturbations which affect the higher excited levels are discussed.

The electric quadrupole fundamental (v=1

The two isotopic forms of stibine, 121 SbH 3 and 123 SbH 3 , have been spectroscopically studied with high resolution. Pure quadrupole resonances both in the ground and in the v 4 = 1 states have been observed using the infrared-radiofrequency double resonance technique in a CO 2 laser cavity. Characteristic hyperfine patterns resulting from direct l -type doubling transitions in the v 4 = 1 state have been measured by microwave spectroscopy. The hyperfine pattern in the ground state is reproduced following the standard treatment. Strong vibration-rotation interactions between the v 2 = 1 and v 4 = 1 states affect the observed spectrum in the v 4 = 1 state. A refined treatment of the vibration-rotation interactions between the hyperfine levels in this state was necessary in order to adequately analyze the experimental data. Quadrupole interaction parameters for a degenerate state of a symmetric-top molecule have been determined for the first time.

In this note we report the observation of 63 pure rotational lines in the spectral region 1.5-4.1 THz with Doppler-limited resolution and very high accuracy

Absorption spectra of C2H2 have been recorded between 50 and 1450 cm−1, with a resolution always better than 0.005 cm−1, using two different Fourier transform spectrometers. Analysis of the data provided two sets of results. First, the bending levels with Σt Vt(t = 4, 5) ≤ 2 were characterized by a coherent set of 34 parameters derived from the simultaneous analysis of 15 bands, performed using a matrix Hamiltonian. The following main parameters were obtained (in cm−1): ω40 = 608.985196(14), ω50 = 729.157564(10); B0 = 1.17664632(18), α4 = −1.353535(86) × 10−3, α5 = −2.232075(40) × 10−3; q40 = 5.24858(12) × 10−3, and q50 = 4.66044(12) × 10−3, with the errors (1σ) on the last quoted digit. Second, a more complete set of bending levels with Σt Vt ≤ 4, some of which have never previously been reported, and also including V2 = 1 have been fitted to 80 parameters. This simultaneous fit involved 43 bands and used the same full Hamiltonian matrix. Some perturbations which affect the higher excited levels are discussed.

The far-infrared spectrum of 15 ND 3 was recorded in the region between 30 and 210 cm −1 at a resolution of 0.002 cm −1 . Inversion-rotation transitions, Δ J = +1, Δ K = 0, a ← s , and s ← a were measured and assigned with J ″ ranging from 2 to 19. Fifty-one Δ J = Δ K = 0, a ← s , pure inversion transitions up to J = K = 18 were measured in the region between 1300 and 2300 MHz; 34 of these were observed for the first time. All these transitions, together with the J = 1 ← 0 and J = 2 ← 1 inversion-rotation transitions reported in the literature, were analyzed simultaneously on the basis of an inversion-rotational Hamiltonian which included Δ k = ±3 and Δ k = ±6 interaction terms. The obtained ground state spectroscopic parameters reproduce the transition frequencies within the accuracy of the measurements.

The high resolution IR Fourier transform spectrum of 13CD3OH was recorded in the region between 910 and 1070cm−1. By using all the previously known spectroscopic data of 13CD3OH, we determined the frequency and the J quantum number for the multiplets of the P and R branches of the CO stretching fundamental band. Transitions in coincidence with the line frequencies of a waveguide CO2 laser were also identified.