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This paper describes a novel approach for empirical lower state assignments in complex high resolution ro-vibrational overtone spectra of molecules with low rotational constants and complex intramolecular dynamics. Methanol, CH3OH, was chosen as a representative of such molecules - it is an asymmetric top with two non-hydrogen nuclei and hindered internal rotation leading to dense and disordered rotational structure of vibrational overtone bands. We report the first rotationally resolved methanol spectra of the OH-stretch overtone 2ν1 band using sub-Doppler diode laser spectroscopy in a supersonic jet, and describe how the combination of two temperature analysis (TTA) and analysis by ground state combination differences (GSCDs) is used to reliably identify spectral lines that originate from lowest rotational states. In the first step of the analysis, the TTA was utilized to obtain a set of possible rotational assignments for each spectral line using the line intensity variation between two different temperatures in the supersonic jet (13, and 56 K respectively). Thereafter, the GSCDs were used to confirm specific lower state assignment for those spectral lines that have been identified to have low rotational ground states by the TTA. We show that the TTA pre-selection leads to fast and reliable confirmation by GSCDs and avoids false assignments due to accidental GSCD matches. The procedure yields an important subset of reliably assigned spectral lines in the complex ro-vibrational structure that provides a convenient starting point for subsequent application of traditional spectral analysis techniques.

International audience; Complete 12CH4 spectrum in the lower icosad spectral range (7050-7350 cm‑1) has been measured in supersonic jet at 28 K for the first time using direct absorption tunable diode laser spectrometer. Due to efficient rotational cooling only spectral lines with lower rotational quantum number J < 4 are observed in the spectrum. Spectral lines in the supersonic jet spectra have been matched with those in liquid nitrogen cooled cell spectra (81 K) and two-temperature method for empirical lower state rotational quantum number assignments has been applied to obtain accurate experimental values of the lower state rotational quantum numbers J″. Especially positions of lines with of J″ = 0 are relevant for vibrational band origin determination, as they are unambiguously the R(0) transitions of the respective bands.

The degenerate combination level ν3 = ν5 = 1 (1669.09 cm−1, E symmetry) was investigated with high-resolution, using a Fourier-transform infrared spectrum recorded in the 1600–1800 cm−1 region, at a resolution of 0.0024 cm−1. A second spectrum, recorded in the 900–1100 cm−1, at a resolution of 0.0024 cm−1, was employed to analyze the ν3 + ν5 − ν3 hot band. The studied combination level has to be treated as a part of a polyad including two other dark states: (ν3 = 1, ν6 = 2, l6 = 0, ∓ 2) and (ν4 = ν6 = 1). The important anharmonic, Coriolis, and α-resonance interactions were extrapolated from the previously studied dyads ν5/2ν6 and ν4/ν3 + ν6. The reproduction thus achieved is quantitative for all the assigned data and provides spectroscopic parameters which are consistent with those of the system of vibrational levels ν5/2ν6.

The degenerate combination level ν 2 = ν 6 = 1 (1611.84 cm −1 , E symmetry) of DCF 3 was investigated with high-resolution using a Fourier-transform infrared spectra. They were recorded in the regions of the combination band between 1550 and 1650 cm −1 and the corresponding hot band ν 2 + ν 6 − ν 6 between 1070 and 1150 cm −1 . The analysis justifies the use of an isolated vibrational level model which yields a fully quantitative reproduction of all assigned experimental data.

The degenerate fundamental vibrational level v5 = 1 (975.51 cm−1, E symmetry) and the overtone vibrational level v6 = 2 (1004.06/1005.98 cm−1, A1 + E symmetry) were reinvestigated with inclusion of their inter-vibrational couplings: the anharmonic Fermi interaction ( Δ K = 0 , Σ t Δ l t = Δ l 5 + Δ l 6 = ± 3 ), the second-order Coriolis resonance ( Δ K = ± 1 , Σ t Δ l t = ± 1 ), and the second-order α-resonance ( Δ K = ∓ 2 , Σ t Δ l t = ± 1 ). This required significant extension of assignments to high J and K rotational states where resonant crossings due to the latter two interactions occur. The newly assigned data from Fourier-transform IR spectroscopy were combined with rotational and laser-sideband rovibrational data pertaining to the v5 = 1 vibrational level, which were used already in a previous analysis, in a fully quantitative simultaneous fit.

The parallel vibration-rotation band ν(4) of methyl isocyanide (CH(3)NC), with a band center at 944.9 cm(-1), was studied by FTIR spectroscopy between 890 and 980 cm(-1) in order to improve the ground-state rotational constants. Such improvement is essential for the scheduled studies of excited vibrational levels and their mutual anharmonic resonances occurring at higher values of the K rotational number. Ground-state combination differences generated from this band, spanning values of J/K from 0 to 85/13, were combined with rotational data from the literature and newly measured rotational transitions, extending the J/K range from 3/0 up to 31/14, and fitted simultaneously with a fully quantitative reproduction of the data. The infrared data of the ν(4) band were analyzed together with rotational data of the ν(4) = 1 level, spanning values of J/K from 4/0 to 14/12. The fit in the approximation of an isolated vibrational state, with the transitions perturbed by weak local resonances excluded, yields reproduction of the data within experimental uncertainties.

International audience; The infrared spectrum of the fluorocarboxyl radical, FCO2, was recorded at high resolution (0.0035 cm−1) in the 600−1400 cm−1 region on a Bruker IFS 120 HR Fourier transform spectrometer of the University of Wuppertal. The analysis of the A-type nu2 band of FCO2 (CF stretching mode) centred at 970.208 cm−1 was performed taking use of the ground state parameters achieved by Kolesnikova et al. [Kolesnikova L, Varga J, Beckers H, Simeckova M, Zelinger Z, Nova Striteska L, Kania P, Willner H, Urban S. J. Chem. Phys. 128, 2008, pp. 224302-1-8]. For the FCO2 radical, the nu2 transitions are, in principle, splitted into two spin - rotation subcomponents corresponding to J= N +/-1/2. However the spin- rotation parameters in the 21 vibrational state have values similar to those of the ground state, and spin-rotation doublings are observable only for the weaker transitions involving medium Ka or Kc values in the P and R branches. The nu2 fundamental band is weakly perturbed by the 2nu5 dark overtone band at 965.4 cm−1 and the 21 and 52 energy levels of FCO2 are coupled through Fermi type resonances. The final energy level calculation was performed accounting both for the spin -rotation interaction within the 21 and 52 vibrational states, and the 21 52 Fermi-type resonances.

The high-resolution infrared spectrum of deuterated fluoroform (DCF3) was studied in the 700 and 1200 cm−1 regions, with the aim of assigning and analyzing the ν4 CF3 asymmetric stretching vibration. The Fermi-type anharmonic coupling between the ν4 = 1 and ν3 = ν6 = 1 rovibrational levels, already mentioned in an early work of Ruoff et al. [Spectrochimica Acta Part A 31A (1975) 1099–1100], was studied here for the first time under high resolution. Assignments in the ν3 + ν6/ν4 band system were confirmed and extended by the identification of the ν3 + ν6 − ν6 and ν4–ν6 bands in the 700 cm−1 region, the latter being enhanced near the Fermi crossings of the studied levels. Data from both the hot and difference bands were included in the analysis. The close separation of the studied vibrational levels of about 14.8 cm−1 produces a large variety of resonance crossings which involve levels with Δ k = 0 , … , 6 . Besides the Fermi ( Δ k = 0 , Δ l = 0 ) and Coriolis ( Δ k = ± 1 , Δ l = ∓ 2 ) resonances, they were accounted for by inclusion of additional higher-order ( Δ k = ± 2 , Δ l = ± 2 and Δ k = ± 3 , Δ l = 0 ) interaction terms between the vibrational states. The least-squares fit of more that 16,000 vibration-rotation transitions provides a quantitative reproduction of data in all bands.

The study of vibration resonance physics in propyne is based on experimental measurements of about 600 new rotational transitions between 495–590 and 700–760 GHz in excited vibrational levels v 5 = 1, v 8 = 1, v 10 = 3 and v 9 = v 10 = 1 with vibrational energies around 1000 cm −1 . The limits to the assignments and analysis were imposed by as yet unresolved anharmonic resonances with the states of the next higher polyad of levels lying above 1200 cm −1 , which affect the rotational states involved in transitions that would be measurable with non-vanishing intensities. Vibration–rotation spectra pertaining to the levels in question were studied in the regions 880–1150 cm −1 (the ν 5 and ν 8 fundamental bands), 550–750 cm −1 (the v 9 = v 10 = 1 ← v 10 = 1 hot bands) and 250–400 cm −1 (the v 10 = 3 ← v 10 = 2 “superhot” bands). A simultaneous least-squares fit of both types of data provides their reliable but in the case of accurate rotational data not always fully quantitative reproduction.

The rotational spectrum of NSF3 in the ground and v5 = 1 vibrational states has been investigated in the centimeter- and millimeter-wave ranges. R-branch (J + 1 (kl = +1, A2) with J (kl = -2, A-), (kl = +4, A+) (kl = +1, A-), (kl = +2) (kl = -1), (kl = +3) (kl = 0), (kl = +2) (kl = -3), and (kl = +3) (kl = -3). The various aspects of the regional resonances are discussed in detail. An accidental near-degeneracy of the kl = 0 and kl = -4 levels at J = 26/27 led to the observation of perturbation-allowed transitions following the selection rule delta(k-l) = +/-6 with (kl = +2) (kl = -4). A corresponding near-degeneracy between kl = -1 and kl = -3 levels at J = 30/31 led to the detection of similar transitions, but with (kl = +3) (kl = -3). In the range 230-480 GHz, R-branch rotational transitions have been measured by absorption spectroscopy up to J = 49 in the ground-state and up to J = 50 in the v5 = 1 vibrational state. The transition frequencies have been analyzed using various reduced forms of the effective Hamiltonians. The data for the v5 = 1 vibrational state have been fitted successfully using two models up to seventh order with delta k = +/-3 interaction parameters constrained (dt constrained to zero, and epsilon to zero or to the ground-state value). On the other hand, reductions with the (delta k = +/-1, deltal = -/+2) interaction parameter q12 fixed to zero failed to reproduce the experimental data since the parameters defining the reduction transformation do not arise in the correct order of magnitude. The ground-state data have been analyzed including parameters up to fourth order constraining either parameters of the delta k = +/-3 interactions to zero (reduction A), or of the delta k = +/-6 interactions to zero (reduction B). The unitary equivalence of the different parameter sets obtained is demonstrated for both vibrational states.

We have developed advanced graphical software for significantly accelerated and verified assignments of rotationally resolved rovibrational molecular spectra. The program combines the traditional approach of Loomis–Wood diagrams, which are used to visualize spectral branches and facilitate their identification, with the power of interactive combination difference checking, which provides an immediate verification of correct assignments of quantum numbers to spectral lines. Assignment procedures and other tools of the program are designed in a fully graphical Windows environment to accelerate the usually tedious assignment work and make the use of the program highly intuitive. The use of an appropriate rovibrational Hamiltonian for fitting the assigned transitions is made easy by the flexible, user-programmed interfaces for exporting assigned data directly in the needed format and importing rovibrational energies back to the assignment program. The program is designed for the MS Windows operating systems and is available upon request with a full documentation on http://www.lww.amu.edu.pl .

The high-resolution infrared spectra of trifluorophosphine (PF3) were reinvestigated in the ν4 fundamental region near 350 cm−1, and around 690 cm−1, with the aim to provide a necessary reassignment of the 2±2 sublevel of the v4 = 2 overtone level. The present paper reports on the first complete study of both sublevels of v4 = 2 (of A1 and E symmetry, corresponding to l4 = 0 and ±2, respectively), through the high-resolution analysis of the overtone 2 ν 4 0 band and the 2 ν 4 ± 2 - ν 4 ± 1 hot band. The assignments of the latter were corrected and extended, spanning the rotational states J ⩽ 82 and −80 ⩽ K″ · ΔK ⩽ 48. These new infrared assignments in the v4 = 2 state were combined with accurate infrared, radiofrequency, centimeter-, millimeter- and submillimeter-wave data of the v4 = 1 level (Thiessen et al., 2000), together with rotational data in the ground vibrational state (Cotti et al., 1995), in a simultaneous fit. The existence of resonance crossings due to a Δk = ±1, Δl = ∓2 l-type resonance in the v4 = 1 state, which generated perturbation-allowed transitions, provided independent values of the C4 and Cζ4 constants. Combining these rotational transitions with the wavenumbers of the ν4 fundamental band enabled us to determine accurately the C0 axial ground state constant. Moreover, the assignment of a few, very weak rRK transitions in the 2 ν 4 - 2 overtone band and their inclusion in the global least-squares fit allowed also the first accurate experimental determination of D K 0 . The obtained results are (in cm−1): C0 = 0.159970241(29) and D K 0 =1.80457(49) × 10−7. Quadratic, cubic, and semidiagonal quartic force fields of PF3 have been calculated at the CCSD(T) level of theory employing a variety of large correlation-consistent basis sets. These force fields have been used to evaluate spectroscopic constants which are generally found to be in very good agreement with experiment. The present best estimate of the re structure of PF3 based on an explicitly correlated coupled-cluster approach (CCSD(T)-F12b) is almost identical with its latest experimental counterpart.

The direct l -type resonance spectrum of CF 3 CCH in the vibrational state ν 10 = 2 has been measured by means of waveguide microwave Fourier transform spectroscopy in the range 8–26 GHz. Two types of direct l -type resonance transitions induced by the (Δ k = ±2, Δ l = ±2) interaction could be observed: 262 transitions following the Δ J = 0, Δ k = Δ l = 2 selection rule covering values of J = 17–64 and G = ∣ k − l ∣ from 2 to 15, and 75 transitions following the Δ J = 0, Δ k = Δ l = 4 selection rule covering values of J = 44–70 and G up to 3. The strong (2, 2) resonance furthermore allowed the observation of A 1 –A 2 splittings of the k = l = ±2 states from J = 63–70. The transitions with G = 3 showed splittings due to the (4, −2) and (0, 6) interactions. The corresponding energy level systems and part of the Hamiltonian matrix are discussed. Strong perturbations due to Δ( k − l ) = 3 interactions coupling the states k = ±1, l = ±2 and k = ±4, l = ±2 made possible the observation of perturbation-allowed transitions with selection rule k = ±1, l =± 2 ↔ k = 0, l = ±2. Additionally, the J = 2–1 and 3–2 rotational transitions have been measured. A multiple fitting analysis has been performed in which the experimental data have been fitted using five reduced forms of the effective Hamiltonian as proposed by Sarka and Harder [J. Mol. Spectrosc. 197 (1999) 254]. Parameters up to sixth order have been determined including the axial rotational constant A for both values of ∣ l ∣ and the unitary equivalence of the determined parameter sets has been demonstrated.

Fourier-transform infrared (IR) spectra between 1235 and 1680 cm−1 and millimeter wave spectra between 198 and 455 GHz of monoisotopic 13CH3 37Cl have been recorded and analysed simultaneously, taking into account all Coriolis, α-resonance, and l-type interactions in the polyad of the ν2=1, ν5=1 and ν3=2 levels. Several α-resonances (Δ k = ±2,Δ l = ∓ 1) generating perturbation-allowed transitions have been assigned both in the rovibrational and rotational spectra. This enabled us to determine accurately and independently A 0= 5.2057128 (72) cm−1, = 8.3968 (105)×10−5 cm−1, and even = 3.95 (38)× 10−9 cm−1. With 52 upper state parameters varied, more than 5300 IR wavenumbers and 162 rotational frequencies pertaining to the excited vibrational states were fitted within their experimental accuracy. The textbook example of a first-order Coriolis resonant crossing between the A and E fundamental vibrational levels (ν2=1 and ν5=1) is discussed in detail with implications for the structures of the corresponding pa...

More than 700 new pure rotational transitions (Δν=0, ΔJ=1, Δk=0) pertaining to the vibrational states ν 10=1, 2 and ν 9=l have been recorded between 85 and 922GHz corresponding to 4≤J″≤53. In the case of ν 10=1, high-K transitions could be recorded up to Kl 10=−17 and +19, respectively, only limited by the vanishing intensities of these lines involving highly excited states. Similarly, the ν 9=1+1 subbranch could be followed up to K=18. Investigations of the other subbranches were limited to K values below those severely perturbed by Fermi interactions with vibrational states of the next tetrad approximately 350cm−1 higher in vibrational energy. Moreover, perturbations in the K=8 stack of ν 5=1 could be traced to a intervibrational q 12 resonance with ν 10=2−2, K=9. Several highly perturbed transitions, including transitions between the two vibrational states, have been recorded in the submillimetre range and fit to within experimental uncertainties. The intervibrational transitions also permitte...

Almost 300 new rotational transitions within the fundamental vibrational level v 10 =1 of propyne have been measured in selected regions between 495 and 925 GHz spanning the quantum numbers 28≤ J ≤54 and 0≤ K ≤16. The accuracies are mostly between 10 and 20 kHz. In addition, the J ″=4 and 5 transitions near 85 and 103 GHz have been remeasured. Simultaneous analyses with refined rovibrational data have been performed, showing that even this lowest and seemingly isolated vibrational level needs a global treatment when high K transitions are involved. The global model with the v 10 =1 level coupled to the next higher cluster of levels, v 10 =2/ v 9 =1, by Fermi and Coriolis resonances is necessary for a quantitative reproduction of both the rovibrational and rotational data within their experimental uncertainties. Included are also improved ground state spectroscopic parameters from a fit of previous pure rotational data and Δ k =3 ground state combination loops as well as additional data obtained in course of the present study.

The υ6=2 vibrational state of the main isotopomer of trifluorosilane, 28SiHF3, has been investigated in the centimeter- and millimeter-wave ranges. Rotational spectra following the Δ J=1, Δk=Δ l=0 selection rule have been measured up to J=24 and K=23 and for both values of ∣l∣. Two types of direct l-type resonance transitions induced by the (Δ l=Δk=±2) interaction could be observed by means of waveguide Fourier transform microwave spectroscopy in the range 8–26 GHz: 252 transitions following the Δ J=0, Δl=Δk=±2 selection rule covering values of J=7–39 and G=∣k-l∣ from 1 to 18 and 90 transitions following the Δ J=0, Δl=Δ k=±4 selection rule covering values of J=17–52 and G from 1 to 4. Due to the strong (2,2) resonance, 18 A1–A2 splittings of the k=l=±2 states from J=36–53 could also be observed. Accidental near-degeneracies lead to strong perturbations due to Δ (k-l)=±3 interactions, enabling the observation of perturbation-allowed transitions with selection rules k=±3(l=±2)↔±4(±2), ±2(±2), A+↔ ±1(∓2), A− and ± 1(0)↔± 6(±2). In a multiple-fit analysis the experimental data have been refined using five reduced forms of the effective Hamiltonian as proposed by Sarka and Harder [J. Mol. Spectrosc.197, 254–261 (1999)]. Parameters up to seventh order have been determined including the axial rotational constant C for both values of ∣l∣ and the vibrational separation of the ∣l∣=0 and 2 states. The unitary equivalence of the determined parameter sets has been demonstrated up to fifth order. Differences of the rotational constants in the various parameter sets have been explained by the theory of reduction. Sign relations of the fitted parameters and general features of the direct l-type resonance spectrum in a υt=2 level are discussed.

The ν 1 (A 1 , 1578.31 cm −1 )/ν 4 ( E , 1615.17 cm −1 ) Si–D stretching dyad of D 3 SiF has been studied by FTIR spectroscopy with a resolution of 2.4×10 −3 cm −1 . Only weak interactions of Coriolis (Δ K =±1, Δl=±1) and α resonance (Δ K =±2, Δl=∓1) type between ν 1 and ν 4 , and of l (2,−4) type within ν 4 , were revealed. However, the v 1 =1 and v 4 =1 levels were found to be severely perturbed by the v 3 = v 5 =1 ( E , 1590.37 cm −1 ) and v 2 = v 3 =1 ( A 1 , 1604.25 cm −1 ) states. These perturbations are observable only near level crossings involving strong Coriolis and α interactions. The energy structure within these perturbers is severely complicated by strong Coriolis and α resonances and by l (2, 2), l (2,−1), and l (2,−4) interactions as already revealed by the ν 2 ( A 1 , 710.16 cm −1 ) and ν 5 ( E , 701.72 cm −1 ) fundamentals. Interactions of the perturbing states with the ν 1 /ν 4 dyad are particularly evident in local crossings. In total, 12 transitions belonging to the dark states and 68 perturbation-allowed transitions within the ν 1 /ν 4 dyad have been detected among the more than 5000 transitions that have been assigned for the ν 1 /ν 4 dyad, with J max and K max of 50 and 30, respectively. Altogether about 85% of the assigned transitions were fitted with a standard deviation of 0.221×10 −3 cm −1 , leading to 61 parameters of the interacting polyad.

The high-resolution infrared spectrum of DCF 3 was investigated in the 2000 cm −1 region, with the aim of assigning and analyzing the overtone bands 2ν 5 ( A 1 + E ), as well as the combination band ν 2 + ν 5 ( E ). The present paper reports on the first high-resolution study of the v 2 = v 5 = 1 and v 5 = 2 levels, through the analysis of the combination ν 2 + ν 5 and the overtone 2 ν 5 ∓ 2 bands respectively. This analysis can be thought of as a necessary step toward the reinvestigation of the complicated vibrational pattern in the CD stretching fundamental region.

High-resolution (ca. 5 x 10(-3) cm(-1)) infrared spectra of monoisotopic samples of F(35)Cl(16)O(3), F(37)Cl(16)O(3), F(35)Cl(18)O(3), and F(37)Cl(18)O(3) have been recorded in the region of the nu(6) fundamental band. This band is centered at 405.6055, 405.5097, 390.5406, and 390.4984 cm(-1), respectively. About 1000 nonzero-weighted transitions were fitted for each isotopomer with an isolated band model, obtaining a s.d. on the residuals close to the experimental precision. Three different reductions of the Hamiltonian have been tested and found almost equally good, although FClO(3) is a nearly spherical top molecule. Each includes the l(2, 2) interaction and either a d(t) DeltaK = +/-3 interaction term (reduction Q) an epsilon(t) DeltaK = +/-3 interaction term (reduction QD), or an l(2, -1) interaction (reduction D). Good agreement between the theoretical predictions for these reductions and the experimental data is observed. Copyright 1999 Academic Press.

A total of 4892 transition wavenumbers of the nu(2), nu(3), nu(5), and nu(6) fundamental bands of H(3)(12)CF and 1469 frequencies of the rotational transitions in the v(2) = 1, v(3) = 1, v(5) = 1, and v(6) = 1 vibrational states have been fitted simultaneously by taking explicitly into account various Coriolis interactions, l-type interactions, and alpha-resonance terms between and within the vibrational states. The standard deviation of the fit using 71 parameters was 8.10 x 10(-5) cm(-1) for the infrared data and 0.198 MHz for the rotational data. This study clearly shows that in order to obtain a really quantitative fit of the highly precise data of vibration-rotational and rotational spectroscopy, it is necessary to fit all the data simultaneously using a variational approach. The deperturbed values of the upper state rotational constants differ significantly from those obtained previously in fitting the nu(3) and nu(6) bands as isolated bands and the nu(2)/nu(5) bands by a variational approach. This is important for the precise determination of the equilibrium structure of methyl fluoride (J. Demaison, J. Breidung, W. Thiel, and D. Papousek, Struct. Chem., in press). Besides this, the results can be used in further studies of the reduced Hamiltonians for more complicated systems of interacting vibrational levels. Copyright 1999 Academic Press.

High-resolution FTIR spectra of monoisotopic D 3 Si 35 Cl have been recorded in the regions 440–590 cm −1 (ν 3 /ν 6 ) and 900–1100 cm −1 (2ν 6 /ν 3 + ν 6 /2ν 3 ). A detailed rovibrational study was done for the 2ν 0 6 , 2ν ∓2 6 , and 2ν 3 overtone bands and for the 2ν ±2 6 –ν ±1 6 , 2ν 0 6 –ν ∓1 6 , and (ν 3 + ν ±1 6 )–ν ±1 6 hot bands. For the first time the interactions occurring between the v 6 = 2, v 3 = v 6 = 1, and v 3 = 2 levels of any trideuterated silyl halide have been analyzed. The (ν 3 + ν ±1 6 )–ν ±1 6 hot band served to obtain accurate energies of the v 3 = v 6 = 1 level, the ν 3 + ν 6 combination band not being detectable on our spectra. The first experimental determination of A 0 and D 0 K for this molecule was undertaken by a well-established method, using the ν 6 , 2ν ±2 6 –ν ±1 6 , and 2ν ∓2 6 bands. Ground state energy differences Δ K ( J ) = E 0 ( J , K ) − E 0 ( J , K − 3) were calculated for K values from 2 to 16. By a least-squares fit of 163 such differences, the A 0 and D 0 K values thus obtained were (in cm −1 ): A 0 = 1.4278230(8) and D 0 K = 5.3916(31) × 10 −6 .

The degenerate combination levels of E symmetry v 3 = v 4 = 1 (1900.21 cm −1 ) and v 3 = 2, v 6 = 1 (1889.30 cm −1 ) were investigated for the first time with high-resolution, using a Fourier-transform infrared spectrum recorded in the 1600–2000 cm −1 region, at a resolution of 0.0024 cm −1 . These combination levels strongly interact through a Fermi-type anharmonic coupling, which plays an essential role in the studied system. Besides the Fermi-interaction, the other important Coriolis (Δ k = ±1, Δ l = ∓2) and higher-order (Δ k = Δ l = ±2) inter-vibrational interactions were also considered, in a similar manner as in the lower ν 3 + ν 6 / ν 4 dyad [P. Pracna et al., J. Mol. Spectrosc. 259 (2010) 1–10]. The fitted wavenumbers of the rovibrational transitions of the ν 3 + ν 4 and 2 ν 3 + ν 6 bands provide a set of molecular parameters which ensure an accurate reproduction of the spectrum. Moreover, these molecular parameters show good agreement with those of the lower system ν 3 + ν 6 / ν 4 .

The microwave and submillimeter wave spectra of propyne between 17 and 358 GHz were measured and the rotational transitions in thev8= 1 excited vibrational state of the CH3rocking vibration were assigned. About 1050 wavenumbers of the ν8vibration–rotation fundamental band and about 600 wavenumbers of the ν5fundamental band of the[formula]stretching vibration were assigned from the infrared spectrum between 910 and 1130 cm−1which was used previously (G. Graneret al., J. Mol. Spectrosc.161,80–101 (1993)) in the analysis of the combinationv9=v10= 1 and thev10= 3 overtone levels (ν9being the[formula]bending and ν10the[formula]bending vibrations). The rovibrational and rotational data corresponding to the two fundamental levels were analyzed simultaneously in least-squares fits using a model which treats together all the vibrational levels in the region around 1000 cm−1with their strong anharmonic and vibration–rotation resonances. The refined parameters reproduce the infrared and submillimeter wave data of thev5= 1 level with standard deviations of 0.32 × 10−3cm−1and 59 kHz, respectively, while for thev8= 1 level the standard deviations were 0.41 × 10−3cm and 290 kHz. The refined parameters of the combination and overtone levels provide reliable predictions for future submillimeter wave studies.

A high-resolution FT infrared spectrum of H3Si79Br (resolution 0.0022 cm−1) in the region 830-1050 cm−1 was used to analyze the fundamental bands ν2 (A1) and ν5 (E). A total of 4392 transition wavenumbers for ν2 and ν5 have been fitted, together with 632 energy values for the ν3 = 2 level, with a standard deviation of the fit of 0.123 × 10−3 cm−1. A model was used taking into account the strong Coriolis x, y resonance between ν2 and ν5, and also three local resonances: (i) an accidental Coriolis-type resonance of ν5 with 2ν3 (crossing of (kl = −13, ν5 = 1) and (K = 14, ν3 = 2) for J′ between 16 and 17); (ii) an l(±2, ∓1) resonance of the (kl = 2, ν5 = 1) and (kl = −3, ν5 = 1) levels, with a crossing for J′ between 58 and 59; and (iii) an accidental l(∓1, ±2) resonance between ν2 (K = 3) and ν5 (kl = 1, A+ and A−). Some "forbidden" transitions, due to this last resonance, were observed and included in the fit. The I-doubling constant q5 and the Coriolis resonance parameters being strongly correlated, these two resonances cannot be treated independently. Hence, q5 was fixed at zero and a value of 0.09314238(58) cm−1 was obtained for Bζ25.

Millimeter-wave and submillimeter-wave spectra of the rotational transitions in the v 2 = 1 and v 5 = 1 vibrational states of 13 CH 3 F were measured up to 462 GHz. Far-infrared spectra of these transitions were measured in the region 30-65 cm −1 with a resolution of 0.0019 cm −1 using an interferometric spectrometer Bruker IFS 120 HR. Almost 700 lines including 14 lines of the Δ( k − l 5 ) = ±3 perturbation-allowed transitions in the v 5 = 1 state were assigned. Both vibrational states are strongly perturbed, especially by the x , y -Coriolis resonance and "2, −1" l -type interactions. The corresponding spectroscopical parameters were determined by a nonlinear least-squares fit to the experimental data.

The vibration-rotational bands ν 2 and ν 5 of gaseous fluoromethane 13 CH 3 F were measured in the region 1200-1700 cm −1 at an unapodized resolution of 0.0041 cm −1 using an interferometric spectrometer Bruker IFS 120 HR. Almost 3000 lines were assigned including 381 lines of the Δ k = ±2 perturbation-allowed transitions to the doubly degenerate vibrational state v 5 = 1. Combination differences were generated for the ground state from the allowed and "forbidden" transitions of the ν 2 and ν 5 bands. They were used in a simultaneous fit with the previously measured frequencies of the ground state rotational transitions and the combination differences generated from the ν 3 band (D. Papousek, Z. Papouskova, Yen-Chu Hsu, P. Pracna, S. Klee, M. Winnewisser, and J. Demaison, J. Mol. Spectrosc. 159, 62-68, 1993) to improve the values of the ground state spectroscopical parameters of 13 CH 3 F. The upper state parameters were determined by fitting simultaneously the infrared data with the frequencies of the rotational transitions in the v 2 = 1 and v 5 = 1 levels (preceding paper), using a variational approach with the constrained values of the ground state parameters.

The Fourier transform spectrum of the vibration-rotational bands ν 2 and ν 5 of gaseous fluoromethane 13 CH 3 F was measured at an unapodized resolution 0.0041 cm −1 . Among the assigned lines, 102 belonged to the Δ k = ±2 perturbation-allowed transitions to the doubly degenerate vibrational state v 5 = 1. Combination differences were generated for the ground state of 13 CH 3 F from the wavenumbers of the allowed and forbidden vibration-rotational transitions to the v 5 = 1 level. They were used in a simultaneous least squares fit with the previously measured microwave, submillimeterwave, and far infrared transition frequencies of the pure rotational transitions in the ground state and with the combination differences generated from the allowed transitions to the v 3 = 1 state of 13 CH 3 F (Pracna, Klee, Winnewisser, Papousek, Yen-Chu Hsu, and Hann-Sen Chen, J. Mol. Spectrosc. 156, 217-226 (1992). This made it possible to determine precisely for the first time A 0 and D 0 K for 13 CH 3 F: A 0 = (5.1824246 ± 0.0000015) cm −1 , D 0 K = (70.912 ± 0.033) × 10 −6 cm −1 .

International audience; An improved procedure for accurate determination of empirical lower state rotational quantum numbers from molecular absorption spectra is demonstrated for methane. We combine the high resolution absorption spectra in the 7070–7300 cm−1 frequency range obtained in liquid nitrogen cooled cryogenic cell (T = 81 K) and in supersonic planar jet expansion (TR = 25 K). Empirical lower state energies of 59 transitions are determined from the ratio of the absolute absorption line strengths at 25 and 81 K. The procedure relies on the realistic description of rotational state populations in the supersonic jet expansion where non-equilibrium nuclear spin isomer distributions are generated due to the rapid cooling. The accuracy of the experimental determination of the lower state energies with J ≤ 3 is found to considerably improve the results of the same approach applied to spectra at 296 and 81 K. The 59 transitions with determined lower J values provide a good starting point for the theoretical interpretation of the highly congested icosad region of methane. In particular, the centres of nine vibrational bands are estimated from the transitions with J = 0 lower state rotational quantum number.

High-resolution Fourier-transform infrared spectra between 1235 and 1680 cm −1 and subterahertz spectra between 250 and 630 GHz of monoisotopic 13 CH 3 35 Cl have been recorded and analyzed simultaneously, with all Coriolis, α -resonance, and l -type interactions in the polyad of the v 2 = 1, v 5 = 1, and v 3 = 2 levels taken into account. Several α -resonances (Δ k = ±2, Δ l = ∓1) generating perturbation-allowed transitions have been assigned in the rovibrational spectra. These resonances enabled us to determine accurately and independently the ground state rotational and centrifugal distortion parameters A 0 = 5.205 746 9 (55) cm −1 and D K 0 = 8.4404 ( 84 ) × 10 - 5 cm - 1 . Even H K 0 = 8.527 ( 39 ) × 10 - 9 cm - 1 , which is, however, correlated to higher-order α -resonance terms, was determined. With 51 upper state parameters varied, about 5800 rovibrational wavenumbers and more than 550 rotational frequencies pertaining to the excited vibrational states were fitted within their experimental accuracy.

Four vibrational levels in the energy region around 1000 cm(-1) were studied. These were the v(5)=1 and v(8)=1 fundamental levels, both components of the v(9)=v(10)=1 combination level (l(9)=l(10)=+/-1 and l(9)=-l(10)=+/-1), and both components of the v(10)=3 overtone level (l(10)=+/-1 and +/-3). New FTIR spectra with a synchrotron radiation source were recorded in the region of the "superhot" v(10)=3--2 bands, which made possible the first assignment of levels of the v(10)=3(+/-1) sublevel. More than 330 new rotational transitions in the combination and overtone levels were measured by millimeter-wave spectroscopy betwen 50 and 360 GHz. The new data were analyzed simultaneously together with the previously assigned rovibrational data for the fundamental and combination levels and rotational data for the fundamental levels using a global model with all anharmonic, Coriolis, l-type, and alpha-resonances. Significant improvement of data reproduction and very good consistency with the Hamiltonian parameters of the lower vibrational levels v(9)=1 and v(10)=1, 2 were achieved. A strong dependence of the A(v) constant on the l(10) quantum number is found for propyne: this is shown to be characteristic of skeleton C-C identical withC or C-C identical withN bending modes in H(3)CCCH, H(3)CCN, and their fully deuterated species. Copyright 2001 Academic Press.

The nu(5) fundamental band of trifluorosilane-d (SiDF(3)) at 627 cm(-1) was studied for the first time by high-resolution FTIR spectroscopy at a resolution of 2.4 x 10(-3) cm(-1). The analysis was performed simultaneously with available microwave and newly measured submillimeter-wave data in the approximation of an isolated degenerate fundamental level of a C(3 Kv) symmetric top molecule leading to a standard deviation of 0.22 x 10(-3) cm(-1) for the reproduction of the infrared wavenumbers, 36 kHz for the microwave, and 198 kHz for the submillimeter-wave frequencies, respectively. The unitary equivalence between the two reductions (Q and D) of the effective Hamiltonian applied in the analysis is demonstrated. Copyright 2000 Academic Press.

The nu(6) (555.453 cm(-1)), the nu(3) (888.899 cm(-1)), and the very weak 2nu(6) infrared bands (2nu(-/+2)(6) 1101.734 cm(-1), 2nu(0)(6) 1100.102 cm(-1)) for the (28)Si species of D(3)SiF have been recorded with a resolution of 3.3, 2.4, and 5.0 x 10(-3) cm(-1), respectively. Millimeter-wave spectra up to 640 GHz of D(3)SiF in the ground, v(3) = 1, and v(6) = 1 and 2 states were measured. Ground state constants complete up to H constants including the K-dependent parameters A(0), D(0)(K), and H(0)(K) as obtained by the nu(+/-1)(6)/2nu(+/-2)(6)-nu(+/-1)(6)/2nu(-/+2)(6) loop method were determined by a merge of 2388 ground state combination differences with 59 rotational data. The v(3) = 1 and v(6) = 1 and 2 levels appear to be unperturbed intervibrationally for the J and K values that could be accessed. However, Deltal = Deltak = +/-2 and Deltal = +/-2, Deltak = -/+4 interactions affect the v(6) = 1 level while the v(6) = 2 levels undergo three interactions of Deltal = Deltak = +/-2, Deltal = +/-2, Deltak = -/+1 and Deltal = +/-4, Deltak = -/+2 type. Typically, for the different bands, 2000-4000 pieces of infrared data augmented by 36-120 rotational data were fitted together. Owing to the weakness of the 2nu(6) band, the body of v(6) = 2 data was enlarged by energies that are deduced from the 2nu(6)-nu(6) and nu(6) bands and which span in particular high K values. Comparison with available ab initio data derived from the harmonic and anharmonic force fields is made. Copyright 1999 Academic Press.

The Fourier transform infrared spectrum of monoisotopic H3Si79Br (resolution 7.7 x 10(-3) cm-1) was studied from 4200 to 4520 cm-1, in the region of the first overtones of the Si-H stretching vibration. The investigation of the spectrum revealed the presence of two band systems, the first consisting of one parallel (nu0 = 4340.2002 cm-1) and one perpendicular (nu0 = 4342.1432 cm-1) strong component, and the second of one parallel (nu0 = 4405.789 cm-1) and one perpendicular (nu0 = 4416.233 cm-1) weak component. The rovibrational analysis shows strong local perturbations for both strong and weak systems. Seven hundred eighty-one nonzero-weighted transitions belonging to the strong system [the (200) manifold in the local mode picture] were fitted to a simple model involving a perpendicular component interacting by a weak Coriolis resonance with a parallel component. The most severely perturbed transitions (whose ||obs-calc || values exceeded 3 x 10(-3) cm-1) were given zero weights. The standard deviations of the fit were 1.0 x 10(-3) and 0.69 x 10(-3) cm-1 for the parallel and the perpendicular components, respectively. The weak band system, severely perturbed by many "dark" perturbers, was fitted to a model involving one parallel and one perpendicular band, connected by a Coriolis-type resonance. The K" . DeltaK = +10 to +18 subbands of the perpendicular component, which showed very high observed - calculated values ( approximately 0.5 cm-1), were excluded from this calculation. The standard deviations of the fit were 11 x 10(-3) and 13 x 10(-3) cm-1 for the parallel and the perpendicular components, respectively. Copyright 1998 Academic Press.