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Bending vibrational modes are responsible for a relevant fraction of molecular absorption spectra in the mid-infrared region at wavelengths beyond 12 μm. To date, the potential of this region for molecular fingerprinting, high-resolution spectroscopy and frequency metrology has been severely hampered by the lack of widely tunable single-mode lasers, with salt-diode lasers almost disappeared, nonlinear laser sources barely delivering optical powers in excess of few hundreds nanowatt [1] and commercial quantum-cascade-lasers (QCLs) hardly emitting beyond 12 μm in cw mode [2] . Recently, direct frequency comb spectroscopy has conquered such region and showed impressive capabilities to acquire ultrabroad high-resolution spectra till 16.7 μm [3] . Nevertheless, spectroscopic data of high metrological quality have not been reported yet, neither spectra with high quality factor in terms of signal-to-noise ratio per spectral point and number of spectral points per spectral feature.

The first high-resolution infrared spectra of CH2D37Cl have been investigated in the region 650–1100 cm−1 where the lowest fundamental bands ν5 (826.2626 cm−1), ν6 (708.4307 cm−1), and ν9 (986.3405 cm−1) occur. These vibrations perturb each other by different weak interactions and the v5 = 1 and v6 = 1 states were treated according to a model which accounts for a c-type Coriolis resonance. The spectral analysis resulted in the identification of 1664, 2550 and 2657 ro-vibrational transitions for ν5, ν6, and ν9 bands respectively, and to the determination of accurate spectroscopic parameters by using the Watson’s A-reduction Hamiltonian in the Ir representation. The simulations of the ro-vibrational structure of the ν5, ν6, and ν9 bands performed in different spectral regions adequately reproduce the experimental data.

The rotational spectrum of $^{15}$ND in its ground electronic $X^{3}\Sigma^{-}$ state has been observed for the first time. Forty-three hyperfine-structure components belonging to the ground and v = 1 vibrational states have been recorded with a frequency-modulation millimeter-/submillimeter-wave spectrometer. These new measurements, together with the ones available for the other isotopologues NH, ND, and $^{15}$NH, have been simultaneously analysed using the Dunham model to represent the ro-vibrational, fine, and hyperfine energy contributions. The least-squares fit of more than 1500 transitions yielded an extensive set of isotopically independent $U_{lm}$ parameters plus 13 Born--Oppenheimer Breakdown coefficients $\Delta_{lm}$. As an alternative approach, we performed a Dunham analysis in terms of the most abundant isotopologue coefficients $Y_{lm}$ and some isotopically dependent Born--Oppenheimer Breakdown constants $\delta_{lm}$ [R. J. Le Roy, J. Mol. Spectrosc. 194, 189 (1999)]. The two fits provide results of equivalent quality. The Born--Oppenheimer equilibrium bond distance for the imidogen radical has been calculated [$r_e^{BO}$ =103.606721(13) pm] and zero point energies have been derived for all the isotopologues., Comment: 11 pages, 1 figure, 8 tables. Accepted for publication in Phys. Chem. Chem. Phys

We report on a precision spectroscopic study of room-temperature H12C13CH in the 6463–6520 cm − 1 range, using a continuous-wave diode laser phase-locked to a near-infrared optical frequency comb synthesizer stabilized, in turn, against a GPS-disciplined rubidium clock. By tuning the comb repetition frequency, several ro-vibrational transitions in the P and R branches of the 2ν3 overtone band are recorded. Accuracy levels as low as 100 kHz, 5 · 10 − 10 in fractional terms, are obtained in the determination of absolute line-center frequencies. In addition, line intensities are measured for the first time, with a best fractional uncertainty of 1%, and used to retrieve the purely vibrational transition dipole moment in conjunction with the first-order Herman–Wallis factor. Finally, the pressure broadening coefficients γself are also derived for the studied transitions.

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 the ammonia isotopologue (ND3)-N-15 has been investigated by high resolution Fourier transform spectroscopy in the region from 450 to 1600 cm(-1). In total, 2217 transitions involving the (s) and (a) inversion-rotation-vibration levels have been identified and assigned to the v(2) and v(4) bending fundamentals. The assigned transitions have been fitted simultaneously using an inversion-rotation-vibration effective Hamiltonian which includes all symmetry allowed interactions between and within the excited state levels. The adopted model has been successful in rationalizing the complicated energy level pattern. Accurate values for the vibration and rotation spectroscopic constants, including 11 interaction coefficients, have been obtained for both inversion levels of the v(2)=1 and v(4)=1 states. The standard deviation of the fit, 0.00071 cm(-1), is about two times the estimated measurement precision. (C) 2013 Elsevier Ltd. All rights reserved.

The high resolution infrared spectrum of 14ND3 has been re-investigated in the intervals 450 - 1600 cm-1 and 2200 - 2800 cm-1, where the absorption lines of the nu2/nu4/2nu2 and nu1/nu3/2nu4 band systems are located. The analysis of the bending fundamentals nu2 and nu4 has been extended assigning 844 transitions belonging to the 2nu2 and 2nu2 - nu2 cold and hot bands. In total, 3436 transitions, of which 3358 are vibration-rotation-inversion and 78 inversion transitions in the v2 = 1 state [Urban Š et al. J Mol Spectrosc 1984;106:29-37] have been fitted simultaneously. The effective Hamiltonian adopted for the analysis includes all symmetry allowed interactions between and within the studied excited state levels. Accurate values of the spectroscopic parameters for both inversion components of the v2 = 1, 2 and v4 = 1 states have been obtained. The inversion transitions are reproduced at 1.8 times their experimental estimated precision, while the infrared data are reproduced at 1.5 times their uncertainties. The assignments of the stretching fundamentals nu1 and nu3 have been extended to higher J and K transitions. The number of transitions of nu1 has been doubled and it has been increased by 23% for nu3. In addition, 805 transitions reaching the v4 = 20 and 2+2 s, a states have been identified. In total, 2408 transitions of the nu1/nu3/2nu4 band system have been fitted simultaneously. The adopted effective Hamiltonian includes also the Fermi resonance terms between v1 = 1 and v4 = 20 and higher order Coriolis terms between v1 = 1/v4 = 2+2, v3 = 1/v4 = 20, and v3 = 1/v4 = 2+2. The model adopted to rationalize the entangled network of energy levels has been moderately successful. The standard deviation of the fit, 0.0090 cm-1, is 9 times the estimated measurement precision. Finally, an improved set of ground state parameters has been derived.

The 2v(1) (A(1)) Si-H stretching overtone band of HSiD3 has been recorded at a resolution of ca. 0.009 cm(-1) between 4200 and 4400 cm-1. About 790 ro-vibration transitions of the (HSiD3)-Si-28 isotopologue have been assigned, with! up to 24 and K up to 21. The spectrum evidences the existence of several perturbations. The assigned transitions have been analyzed either neglecting or including in the model A(1)/E Coriolis-type interactions between v(1) = 2 and nearby dark states. The standard deviation of all the fits is, however, more than one order of magnitude larger than the estimated experimental precision and is independent of the adopted model. (C) 2012 Elsevier Inc. All rights reserved.

The high resolution infrared spectra of the mono isotopic species (FClO3)-Cl-35-O-16, (FClO3)-Cl-37-O-16, (FClO3)-Cl-35-O-18 and (FClO3)-Cl-37-O-18 have been analysed in the region of the nu(1) + nu(5) perpendicular combination band, from 1540 to 1680 cm(-1). For all the isotopologues the nu(1) + nu(5) band is of medium intensity at the recording conditions. In total, about 2400, 2000, 2600 and 2700 transitions have been assigned for (FClO3)-Cl-35-O-16, (FClO3)-Cl-37-O-16, (FClO3)-Cl-35-O-18 and (FClO3)-Cl-37-O-18, respectively. The data for each band have been analysed on the basis of the usual Hamiltonian for a degenerate state of a molecule of C-3v symmetry. In addition, two interaction terms have been considered active within the v(1) = v(5) = 1 state, with Delta l = 0, Delta k = +/- 3 and Delta l = Delta k = +/- 2 selection rules. The ro-vibration parameters of the v(1) = v(5) = 1 states have been obtained, together with the band origins. Combining the nu(1) + nu(5) origins with those of the nu(1) and nu(5) fundamentals, the anharmonicity constant x(15) has been derived for the four molecules and compared to the corresponding value calculated ab initio.

International audience; The second CH stretching overtone of cyanoacetylene, HC 3N, near 9700 cm -1 has been recorded by Fourier Transform Spectroscopy (FTS) and by Intracavity Laser Absorption Spectroscopy (ICLAS) with a Vertical External Cavity Surface Emitting Laser (VECSEL). In total thirteen bands have been identified in the highly congested spectra and rotationally assigned. Their rovibrational spectroscopic parameters have been obtained from a fit of the line centers.

The high-resolution infrared spectra of the monoisotopic species 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 studied in the region of the 2ν 5 overtones, from 1100 to 1200 cm −1 . Both the parallel 2 ν 5 0 and the perpendicular 2 ν 5 ∓ 2 components are clearly observed in the spectra, their origins differing by about 0.4 cm −1 . In each spectrum about 2000 transitions have been assigned, 35% of them belonging to 2 ν 5 0 . The parallel and perpendicular bands in each manifold have been analyzed separately since no evidence of perturbations has been observed. The rovibration parameters of the v 5 = 2, l 5 = 0 and v 5 = 2, l 5 = ∓ 2 excited states have been obtained. For the four species combining the 2 ν 5 0 and 2 ν 5 ∓ 2 band origins with those of the ν 5 fundamentals the harmonic wavenumbers, ω 5 0 , and the x 55 and g 55 anharmonicity constants have also been derived.

The infrared spectra of the 2ν1, 2ν2 and 2ν3 overtones of perchloryl fluoride, FClO3, have been recorded at high resolution using monoisotopic pure samples. Four symmetric top species have been investigated: F35Cl16O3, F37Cl16O3, F35Cl18O3 and F37Cl18O3. The vi = 2, i = 1, 2, 3 vibrationally excited states are totally symmetric, so these overtones correspond to parallel bands of medium/weak intensity, centered from 2010 to 2120 cm−1 (2ν1), from 1390 to 1430 cm−1 (2ν2) and from 1070 to 1100 cm−1 (2ν3). Most of the bands are unperturbed and their analysis was straightforward. The band origins, the rotational and centrifugal molecular constants in the v1 = 2, v2 = 2 and v3 = 2 states have been determined, with standard deviations of the fits from 0.00024 to 0.00067 cm−1. The 2ν1 overtones of F35Cl16O3 and F37Cl16O3 are perturbed by an A1/E Coriolis resonance between the v1 = 2 state and one E component of the v4 = 1, v6 = 2 manifold. The 2ν2 of F37Cl18O3 is perturbed by the same kind of interaction involving the v1 = v6 = 1 (E) state, at about 1396 cm−1. In these bands the resonance is localized on rotational levels with specific J and K values. As a consequence, a few transitions of the perpendicular bands involving the interacting levels could be identified in the spectra. A simultaneous fit of the transitions assigned to the dyads has been performed and the parameters of the excited states have been determined, including the high order Coriolis interaction coefficient C 11 1 . The anharmonic constants x11, x22, x33 of all the studied isotopologues of FClO3, x46 of F35Cl16O3, x46 + g46 of F37Cl16O3 and x16 of F37Cl18O3, have been derived.

The high resolution infrared spectrum of mono-isotopic F 37 Cl 16 O 3 has been studied in the regions of ν 1 , ν 2 , ν 4 and ν 2 + ν 5 bands, centered at 1060.20, 707.16, 1301.71 and 1292.15 cm −1 , respectively. The ν 1 and ν 2 parallel bands are unperturbed so their analysis was straightforward and 3355 and 2433 transitions were assigned, respectively. The band origins, the rotational and centrifugal molecular constants in the v 1 = 1 and v 2 = 1 states have been determined, with standard deviation of the fits σ = 0.00019 and 0.00018 cm −1 . The ν 4 fundamental is affected by an anharmonic resonance with the ν 2 + ν 5 combination band. The kl > 0 sublevels cross at kl ⩾ 27 because of the opposite values of A ζ 4 z and A ζ 25 z . The anharmonic resonance constant W 245 F = 2.7991246 ( 358 ) cm −1 has been derived. The Δ l = Δ k = ±2 and Δ l = 0, Δ k = ±3 essential resonances have been found to be effective in ν 4 , while in ν 2 + ν 5 only the Δ l = Δ k = ±2 one was active. A total of 5721 transitions have been assigned, 25% of them belonging to ν 2 + ν 5 . The rovibrational parameters and the interaction constants of F 37 Cl 16 O 3 have been obtained. The standard deviation of the fit is 0.0006 cm −1 , six times the estimated data precision. The equilibrium geometry of perchloryl fluoride has been determined from the A e and B e constants of F 35 Cl 16 O 3 and F 37 Cl 16 O 3 . Using the A 0 and B 0 constants of all the symmetric species the r 0 geometry has also been derived.

The Raman spectrum of 12C2H4 has been recorded in the 1343–1347cm−1, 1617–1626cm−1 and 1651–1664cm−1 regions using an inverse Raman technique with an instrumental resolution of about 3×10−3cm−1. The Q branches of V3 (CH2 bending, Ag) at 1343.31 cm−1, V2 (CC stretching, A g ) at 1626.17 cm−1 and 2v10 (overtone of CH bending in plane, A g ) at 1664.16 cm−1, were observed and analysed. The recorded bands are of type A, and the selection rules for the transitions are ΔJ=0, ΔK a =0 and ΔK C =0 since only Q branches are strong enough to be observed. The v 2 and 2v10 bands are perturbed owing to a Fermi interaction between the V 2 =1 and v10=2 states, the latter being in turn perturbed by the v 7 =v 10=1 state, at about 1780 cm−1, through a z(a)-type Coriolis interaction. The V3 band has been analysed taking into account the y(c)-type Coriolis interaction between the v3=1 and V 6 =1 levels. Although the v6 fundamental and v 7 +v 10 combination bands have not been detected, their origins and rotational c...

The infrared (IR) spectrum of PD 3 has been recorded in the 1580–1800 cm −1 range at a resolution of 0.0027 cm −1 . About 2400 rovibrational transitions with J ′ = K ′ ⩽22 have been measured and assigned to the ν 1 ( A 1 ) and ν 3 ( E ) stretching fundamentals. These include 506 “perturbation-allowed” transitions with selection rules Δ( k − l )=±3. Splittings of the K ′′ =3 lines have been observed. Effects of strong perturbations are evident in the spectrum. Therefore the rovibrational Hamiltonian adopted for the analysis explicitly takes into account the Coriolis and k -type interactions between the v 1 =1 and v 3 =1 states, and includes also several essential resonances within these states. The rotational structure in the v 1 =1 and v 3 =1 vibrational states up to J ′ = K ′ =18 was reproduced by fitting simultaneously all experimental data. Thirty-four parameters reproduced 1950 transitions retained in the final cycle with a standard deviation of the fit equal to 4.9 × 10 −4 cm −1 (about the precision of the experimental measurements).

Infrared spectra of PD 3 have been recorded in the 600 – 1160 cm - 1 range at a resolution of 0.0023 cm - 1 . About 2500 rovibrational transitions have been measured and assigned to the ν 2 ( A 1 ) and ν 4 ( E ) bending fundamentals, including 131 “perturbation allowed” transitions with selection rules Δ ( k - l ) = ± 3 and ± 6 . Splittings of the K ″ = 3 , 6, and 9 lines were observed. The rotational structure in the v 2 = 1 and v 4 = 1 vibrational states up to J = K = 28 was reproduced by fitting simultaneously all experimental data. The adopted rovibrational Hamiltonian explicitly takes into account the Coriolis and k -type interactions between the v 2 = 1 and v 4 = 1 states, and includes also several essential resonances within these states. Two different reductions of the Hamiltonian were adopted in the fitting procedure. The 41 parameters in model 1 reproduced 2435 IR transitions retained in the final cycle with a standard deviation of the fit equal to 2.06 × 10 - 4 cm - 1 (about the precision of experimental measurements); in model 2, 45 parameters reproduced 2428 transitions with the same value of standard deviation. The equivalence of the two sets of parameters has been demonstrated.

The FTIR spectrum of CH2ClF (natural isotopic mixture) was investigated in the ν4, ν9 and ν5 + ν6 band region between 950 and 1160 cm-1 at the resolution of 0.004 cm-1. The ν4 and ν5 + ν6 vibrations of A′ symmetry give rise to a/b hybrid bands with a predominant a-type component. The ν9 vibration of A″ symmetry, expected with a c-type band contour, shows an intense Coriolis-induced parallel component (ΔKa = 0, ΔKc = 0) derived from mixing with the ν4 = 1 vibrational state. The high-resolution spectra of ν9 and ν5 + ν6 have been analyzed for the first time, while the assignments of the ν4 band, previously investigated, have been extended to higher J and Ka values in the b-type component. The spectral analysis resulted in the identification of 1508, 809 and 349 transitions for the ν4, ν9 and ν5 + ν6 bands of CH2 35ClF, respectively. Besides the strong first-order a- and b-type Coriolis resonances between ν4 and ν9, the ν5 + ν6 vibration was found to interact through a c-type Coriolis with the ν4 and 3ν6. High-order anharmonic resonance (ΔKa = ±2) between ν4 and ν5 + ν6 was also established. All the assigned data were simultaneously fitted using the Watson's A-reduction Hamiltonian in the Ir representation and the relevant perturbation operators. The model employed includes five types of resonances within the tetrad ν4/ν9/ν5 + ν6/3ν6. A set of spectroscopic constants for ν4, ν9 and ν5 + ν6 bands as well as parameters for the dark state 3ν6 and seven coupling terms have been determined. The simulations performed in different spectral regions satisfactorily reproduce the experimental data.

Infrared spectra of PD 3 have been measured in the 20–320 cm −1 range and in the region of the ν 2 /ν 4 and ν 1 /ν 3 fundamental bands near 750 and 1690 cm −1 , respectively, with a resolution of ca. 0.0025 cm −1 . Furthermore, submillimeter-wave spectra covering the J =4–3, 13–12, and 14–13 clusters in the vibrational ground state were recorded. The observed Δ J =+1 rotational lines were augmented by about 5500 ground state combination differences formed from transitions belonging to the fundamental bands. Of these, 1300 involved perturbation-allowed lines with Δ K ≠0. These data and observations taken from the literature were appropriately weighted and fitted to 14 ground state molecular constants. The A and B reductions of the rotational Hamiltonian were found to be equivalent. Improved effective ground state and equilibrium structures were determined for both PH 3 and PD 3 ; the equilibrium structures, r e (PH)=141.1607(83) pm and α e (HPH)=93.4184(95)° and r e (PD)=141.1785(57) pm and α e (DPD)=93.4252(68)°, are in good agreement.

We report results from measurements of the high resolution FTIR spectrum for the fully deuterated benzene molecule C6D6 in the range 450–3500 cm−1. Accurate spectroscopic constants have been obtained for the fundamental vibration ν11 at 496.208 cm−1 and improved ground state constants have been deduced from a fit of ground state combination differences. The J structure of the combination parallel bands ν2 + ν11 (at 2798.1 cm−1), ν5 + ν12 (1802.5 cm−1) and ν7, + ν16 (2619.3 cm−1) of C6D6 has been analysed as well, from which improved values of the band origin and of the B and D j constants of the excited states have been obtained. The strongest hot bands accompanying these parallel transitions have been assigned by means of the anharmonic force field calculated by Maslen et al. [1992, J. chem. Phys., 97, 4233]. In particular (ν11 + ν16) − ν16 is assigned to the band at 492.4 cm−1 even though its shape is typical of a perpendicular transition (PAPE). New values for the ν5, ν12 and ν16 band origins are deter...

The harmonic frequencies ω est of 12 C 6 H 6 calculated by combining the anharmonic constants from a DFT quartic force field with the experimental fundamentals, are compared with harmonic frequencies, ω calc , obtained with different theoretical methods. One set of ω calc was derived by Martin, Taylor and Lee by ab initio CCSD(T) theory, the others have been calculated by us by means of the density funcional theory DFT with B3LYP, B3PW91, B3P86 and mPW1PW hybrid functionals. The mean absolute deviation between ab initio ω calc and ω est is 6.8 cm −1 while between DFT ω calc and ω est is between 8.6 and 10.5 cm −1 . Moreover the DFT ω calc show a small systematic underestimation of the CH stretching vibrations.

The high resolution infrared spectra of monoisotopic F35Cl18O3 and F37Cl18O3 have been studied in the region of the ν4 fundamentals, centered at 1278.3 and 1263.3 cm−1, respectively. Large perturbations are observed in both bands due to a Fermi type anharmonic resonance with the ν2 + ν5 combination bands, centered at 1270.7 cm−1 in F35Cl18O3 and 1257.3 cm−1 in F37Cl18O3. In particular, they affect the kl > 0 levels of the v4 = 1 and v2 = v5 = 1 states which cross at kl ⩾ 18 in F35Cl18O3 and kl ⩾ 3 in F37Cl18O3, due to the opposite values of A ζ 4 z and A ζ 25 z . The Δl = Δk = ±2 and Δl = 0, Δk = ±3 essential resonances are also effective in the excited states of the dyad in F35Cl18O3, while in F37Cl18O3 only the Δl = Δk = ±2 one is active. In the spectrum of F35Cl18O3 3423 transitions have been assigned, 10% of them belonging to ν2 + ν5. The rovibrational parameters and the interaction constants between the v4 = 1 and v2 = v5 = 1 levels have been obtained. The depertubed band origins of ν4 and ν2 + ν5 are 1277.310567(165) and 1271.753733(195) cm−1, respectively, and the anharmonic resonance constant W 245 F is 2.804416(153) cm−1. For F37Cl18O3, 3022 transitions have been assigned, 38% belonging to the ν2 + ν5 combination band. The depertubed band origins are 1260.856338(123) and 1259.872338(134) cm−1, for ν4and ν2 + ν5 and the W 245 F constant is 2.9350669(405) cm−1. The equilibrium geometry of perchloryl fluoride, re (ClO) = 139.7(3) pm, re (ClF) = 161.0(5) pm, and αe (OClO) = 115.7(4) degree, has been determined using the Ae and Be equilibrium constants of the four symmetric isotopologues of perchloryl fluoride, F35/37Cl16O3 and F35/37Cl18O3.

The anharmonic force field of benzene has been calculated using a finite difference method by means of density functional theory (DFT) with the B3LYP functional and a TZ2P atomic orbitals basis set, and compared to the field calculated by Maslen et al. [J. Chem. Phys. 97, 4233 (1992)]. The vapor phase infrared (IR) spectra of benzene (natural isotopic mixture) and of 12C-benzene have been recorded from 450 to 6000 cm−1, at resolutions varying from 0.05 to 0.008 cm−1, and at various path lengths (0.18/42 m). The parallel bands ν11, ν4+ν12, ν5+ν12, ν2+ν11, and ν7+ν16, using the Wilson numbering, with their accompanying hot bands, have been analyzed and their origins determined to test our computed anharmonic force field. The Raman spectra of gas-phase benzene have been also recorded at medium resolution (∼0.7 cm−1) using an argon laser (line at 514.5 nm) with a power of 0.8 W and a multipass cell. In this work we compare the experimental and the theoretical frequencies and band profiles of the parallel ν1, ν2, 2ν16, 2ν4, and 2ν14 and of the corresponding hot bands, taking into account the l-vibrational doubling and all Fermi resonances within 100 cm−1. By comparison with experiment, the DFT B3LYP is shown to be more accurate than the self-consistent field (SCF): the fundamentals are calculated with a mean absolute error of 10.7 cm−1 and most of the spectroscopic constants are in better agreement with the experimental values.

Infrared spectra of deuterated monofluoroacetylene, DCCF, have been recorded in the region between 320 and 850cm(-1) at an effective resolution ranging from 0.0024 to 0.0031cm(-1). In total, 6650 rotation vibration transitions were assigned to 37 bands involving the bending states with v(4) + v(5) and |l(4)+l(5)|, respectively, up to 3, allowing the characterisation of the ground state and of 18 vibrationally excited states. The v nu(5) bending fundamental has been studied for the first time. In addition, the difference band v(3)

The v4 fundamental band of CF3 Br-79 and CF3 Br-81, present in natural isotopic abundance, was investigated in the 8.3-m region by high-resolution infrared spectroscopic techniques. Tuneable diode laser spectra were recorded in the ranges 1202.5-1205.0 cm-1, 1208.0-1210.1 cm(-1) and 1212.5-1214.5 cm(-1). The tuneable diode laser spectra were obtained at the reduced temperature of 200 K and in a free-jet expansion. The latter technique was used to reduce spectral congestion, achieving a rotational temperature of about 50 K, with a resolution up to 0.0008 cm(-1). A Fourier transforminfrared spectrumcovering the entire spectral region of the v(4) band, between 1190 and 1220 cm(-1), was recorded at 298 K with a resolution of 0.004 cm(-1). The experimental wavenumbers from the different spectroscopic techniques were combined to accomplish the complete ro-vibrational analysis of v(4). In total, 4651 transitions were assigned to CF3 Br-79, 4047 to CF3 Br-81, with J(max)'' = K-max '' = 80; of these, 3171 for CF3 Br-79 and 2755 for CF3 Br-81 are from diode laser measurements. The data of each isotopologue were analysed using the model Hamiltonian for a degenerate vibrational state of a molecule of C3v symmetry. The v4 band of both the isotopologues resulted essentially unperturbed, but the Delta l = Delta k = +/- 2 l-resonance was found to be active within the v(4) = 1 state. Precise values of the vibrational energy and of the ro-vibrational parameters of v(4) = 1 for CF3 Br-79 and CF3 Br-81 were obtained. The bromine isotopic splitting amounts to 6.9 x 10(-3) cm(-1). In addition, the equilibrium geometry and the harmonic force field were calculated ab initio using the large-size basis set def2-QZVP in conjunction to the PBE0 functional.

The IR spectra of phenanthrene-h10 and -d10 have been recorded in the vapour phase from 200 to 3200 cm−1 with a resolution of 0.2 cm−1, using a multipass cell heated at 90°C. The assignment of the vibrational bands has been performed by comparison with the theoretical spectra, evaluated using Density Functional Theory and Scaled Quantum Mechanical (SQM) force fields. We found that both methods reproduce the sequence of the experimental frequencies to a good accuracy, allowing in most cases consistent and unambiguous assignments. The relative intensities have also been measured and compared with theory.

The ν 1 ( A 1 ) and ν 4 ( E ) Si–H stretching fundamentals of H 3 SiD have been recorded at an effective resolution of 0.006 cm −1 between 2050 and 2300 cm −1 . A total of about 2500 rovibrational transitions of the H 3 28 SiD isotopomer have been assigned with J ′ up to 27 and K ′ up to 22. A large number of “perturbation allowed” Δ k = ±3 transitions have been identified in both the ν 1 and ν 4 bands. The assigned transitions have been analyzed using two different theoretical models, which took into account several rovibrational interactions between and within the v 1 = 1 and v 4 = 1 states, yielding a standard deviation of each fit of ca. 0.0004 cm −1 , which may be compared with the experimental precision (ca. 0.0001 cm −1 ). Improved ground state parameters have also been obtained by means of ground state combination differences.

The IR spectra of anthracene-h10 and -d10 have been recorded for the first time in the gas phase from 450 to 3200 cm−1 with a resolution of 0.2 cm−1, using a multipass cell heated to 100°C. For the assignment of vibrational bands we have evaluated the theoretical spectrum using density functional theory (DFT) and scaled self consistent field force fields. We found that both methods reproduce the sequence of the experimental frequencies to a good accuracy, allowing in most cases consistent and unambiguous assignments. The relative intensities of C14H10 and C14D10 have also been measured and compared to theory.

The infrared spectrum of the perdeuterated acetylene, (C2D2)-C-12, has been recorded from 900 cm(-1) to 5500 cm(-1) by Fourier transform spectroscopy at a resolution ranging between 0.004 and 0.009 cm(-1). Ninety-two bands involving the nu(1), nu(2), and nu(3) stretching modes, also associated with the nu(4) and nu(5) bending vibrations and 9 bands involving pure bending transitions have been observed and analysed. In total, 8345 transitions for the stretching-bending, and 862 for the pure bending modes have been assigned in the investigated spectral region. All the transitions relative to each stretching mode, i.e. the fundamental, its first overtone, and associated hot and combination bands involving bending states up to v(4) + v(5) = 2, were fitted simultaneously. The Hamiltonian adopted for the analysis is that appropriate to a linear molecule and includes vibration and rotation l-type interactions. The Darling-Dennison interaction between v(4) = 2 and v(5) = 2 levels associated with the various stretching states was also considered. The standard deviation for each global fit is smaller than 0.0006 cm(-1), of the same order of magnitude of the measurement precision. (C) 2013 American Institute of Physics.

The FTIR spectra of CH2ClF (natural isotopic mixture) and ClF (isotopically enriched sample) were investigated in the ν5 and 2ν6 region between 700 and 800 cm−1 at a resolution of 0.004 cm−1. The ν5 and 2ν6 vibrations of A′ symmetry give rise to a/b hybrid bands with a very predominant a-type component. Due to the proximity of their band origins, the v 5 = 1 and v 6 = 2 levels perturb each other by Fermi and Coriolis resonances. The interaction mechanisms, previously investigated in the rotational spectra of ClF, were extended to the less abundant isotopic species ClF and to higher J and Ka values in the main isotopologue. The spectral analysis resulted in the identification of 4188 and 5392 transitions for ClF and ClF, respectively. All the assigned data were simultaneously fitted using the Watson's A-reduction Hamiltonian in the I r representation and perturbation operators. Excited state parameters, band origins and coupling terms for the ν5/2ν6 dyad of both isotopologues were determined.

The gas-phase IR spectrum of 1-azaindolizine has been recorded in the range from 100 to 3200 cm–1, at the resolution of 0.05 cm–1, using a multipass cell heated to 80 °C. The spectrum analysis has been performed by comparing the experimental spectrum with the theoretical one, using both frequency and intensity matching as guidelines for the assignments. The theoretical spectrum of 1-azaindolizine has been calculated from the harmonic force field evaluated at the self consistent field (SCF) level followed by empirical scaling according to the scaled quantum mechanical (SQM) approach, with pyridine and imidazole as parent molecules. The final root-mean-square deviation (RMSD) of the computed and experimental frequencies is 18 cm–1.

The gas-phase IR spectrum of 7-azaindole has been recorded from 100 to 4000 cm–1, using a multipass cell heated to ca. 110 °C, and completely assigned using theoretical predictions based on the scaled quantum mechanical (SQM) method. The harmonic force field of 7-azaindole, evaluated at the HF-SCF level using 6-31G** orbitals, is corrected by scaling the force field over a convenient set of internal coordinates. Scaling factors were determined by least-squares fitting of the theoretical to the experimental frequencies of the two parent molecules, pyridine and pyrrole, and their perdeuteriated isotopomers. Our final prediction gives frequencies for 7-azaindole which on average differ from experiment by 18 cm–1.

High resolution infrared spectra of 121SbHD2 and 123SbHD2 have been studied in the region of ν 1 , the Sb–H stretching fundamental, from 1780 to 1990 cm−1. The 2 ν 1 stretching overtone band of 123SbHD2, located in the 3640–3790 cm−1 range, has also been investigated. The SbHD2 molecule is an asymmetric rotor of Cs symmetry with the asymmetry parameter κ = 0.61. The ν 1 band is of hybrid type, formed by strong C-type and weak B-type transitions, and almost unperturbed. For 123SbHD2, 2092 transitions have been assigned: 70% of these belong to the C component, the other 30% are of B-type. The assigned transitions have been fitted using a Watson type S-reduced Hamiltonian in the III l representation, with a standard deviation of the fit σ = 0.45 × 10−3 cm−1. In order to determine the ground state parameters all possible ground state combination differences (GSCD) have been generated from the ν 1 transitions. In total, 3942 GSCD up to J ″ = 27, K a ″ = 25, and K c ″ = 20 have been fitted with σ = 0.52 × 10−3 cm−1. Only C-type transitions have been observed in the weak 2 ν 1 overtone band. The 556 assigned transitions have been fitted with σ = 2.6 × 10−3 cm−1 using the same Hamiltonian as for ν 1 . In the ν 1 band of 121SbHD2 771 C-type transitions have been assigned, and the v 1 = 1 spectroscopic constants obtained from a fit with σ = 0.70 × 10−3 cm−1. Using 618 GSCD the ground state spectroscopic constants of 121SbHD2 have been derived with σ = 1.0 × 10−3 cm−1. The molecular parameters for the ground and the v 1 = 1 states of the two isotopologues agree well. The quartic theoretical ab initio force field of SbH3 has been used to predict all relevant spectroscopic parameters for 123SbHD2, 121SbHD2, 123SbH2D, and 121SbH2D. Relations between the harmonic frequencies and between the anharmonicity constants obtained in the expanded local mode theory, for the XH3 → XH2D/XHD2 isotopic substitution, have been compared with those obtained in the present study.

The microwave spectra of 1H-benzotriazole and its N-D isotopomer and of 1,2,4-triazolo[1,5-a]pyrimidine have been investigated in a heated cell. Both molecules are planar. Their dipole moments have been measured. The rotational spectra of some vibrational satellites belonging to the butterfly and 1,3-twisting vibrations have also been assigned.

The 000 bands in the S1-S0 electronic absorption systems of lH-benzotriazole at 286 nm and of 1,2,4-triazolo[l,5-a]pyrimidine at 315 nm have been analyzed by computer simulation of their rotational contours. The results have shown that the benzotriazole hand is an almost pure type-B band, while in the case of 1,2,4-triazolo[l,5-a] pyrimidine it is a pure type-A band, so each S1-S0 electronic system is assigned as A1A′(ππ*)-X1A′. In both of these molecules, the transition moment is in the molecular plane, almost parallel to the b-inertial axis in benzotriazole. while it is parallel to the a-inertial axis in 1,2,4-triazolo[1,5-a]pyrimidine. Since the S1-S0 transitions in the indole derivatives previously analyzed were shown to be π*-π, it seems likely that the nature of the S1-S0 electronic transition is the same in all the molecules of this kind.

The gas-phase IR spectrum of indazole has been recorded from 100 to 4000 cm–1, using a multipass cell heated to 120 °C, and completely assigned using theoretical predictions based on the scaled quantum mechanical (SQM) method. The single-crystal IR spectrum of this molecule, previously reported, has been compared with our data and partially reassigned. The harmonic force field of indazole, evaluated at the HF-SCF level using 6-31G** orbitals, is corrected by scaling the force field over a convenient set of internal coordinates. Scaling factors were determined by least-squares fitting of the theoretical to the experimental frequencies of two parent molecules, benzene and pyrazole and their perdeuteriated isotopomers. Our final prediction gives frequencies for indazole which, on average, differ from experiment by 24 cm–1. We confirm the validity of the SQM method as a practical tool for a complete analysis of vibrational spectra, even for molecules of this complexity.

The microwave spectrum of indazole and its ND isotopomer has been investigated at 70°C. The tautomer with the NH group closer to the phenyl ring is found to be the more stable both by the analysis of the rotational spectrum and ab initio calculations. The second tautomer is calculated at HF/4–21G level of theory to be 2800 cm−1 higher in energy. Information on the dipole moment and the low energy vibrational excited states has also been obtained.

The microwave spectra of benzimidazole and of its N-D monodeuterated isotopic species, obtained at 120°C, show the full planarity of the molecule. Information on the lower energy vibrational excited states, and on the dipole moment have also been obtained.

The microwave spectra of 1H-benzotriazole and its N-D isotopomer and of 1,2,4-triazolo[1,5-a]pyrimidine have been investigated in a heated cell. Both molecules are planar. Their dipole moments have been measured. The rotational spectra of some vibrational satellites belonging to the butterfly and 1,3-twisting vibrations have also been assigned.

The gas-phase IR spectrum of 1-azaindolizine has been recorded in the range from 100 to 3200 cm–1, at the resolution of 0.05 cm–1, using a multipass cell heated to 80 °C. The spectrum analysis has been performed by comparing the experimental spectrum with the theoretical one, using both frequency and intensity matching as guidelines for the assignments. The theoretical spectrum of 1-azaindolizine has been calculated from the harmonic force field evaluated at the self consistent field (SCF) level followed by empirical scaling according to the scaled quantum mechanical (SQM) approach, with pyridine and imidazole as parent molecules. The final root-mean-square deviation (RMSD) of the computed and experimental frequencies is 18 cm–1.

The high resolution infrared spectrum of the mono-isotopic species F35Cl16O3 has been studied in the region of the 2ν4 overtone, from 2560 to 2680 cm−1. The 2 ν 4 ∓ 2 perpendicular component is strong and clearly observed while the 2 ν 4 0 parallel component is very weak and almost completely hidden by the perpendicular one. Their origins differ by 12.6 cm−1, the 2 ν 4 ∓ 2 being located at higher wavenumbers. The 2 ν 4 ∓ 2 band is perturbed by the anharmonic interaction between the v4 = 2, l4 = ∓ 2 and v2 = v4 = v5 = 1, l4 = l5 = ± 1 excited states, both of E symmetry. In total 3157 transitions have been assigned, 83% of these to 2 ν 4 ∓ 2 , 12% to ν 2 + ν 4 ± 1 + ν 5 ± 1 , and 5% to 2 ν 4 0 . The three bands have been analyzed simultaneously, taking into account the Fermi resonance effective between the excited states of E symmetry. The ro-vibration parameters of the excited states have been obtained, including the deperturbed band origins of 2 ν 4 ∓ 2 and ν 2 + ν 4 ± 1 + ν 5 ± 1 , at 2628.5890(4) and 2619.3342(5) cm−1, respectively. The W 245 anharmonic constant is equal to 4.0161(4) cm−1. The x 44 + g 44 and x 24 + x 45 + g 45 anharmonicity constants have been derived from the obtained band origins and those of ν4 and ν2 + ν5.

The 0 0 0 band of the S 1 - S 0 electronic absorption system of indazole at 290 nm has been analyzed, and the results of the computer simulation of its rotational contour have shown that this band is and A B hybrid with an intensity ratio A B = 1.22 . The S 1 - S 0 electronic system is assigned as A 1 A ′(ππ ∗ )- X 1 A′ . The same result has already been reached for benzimidazole (E. Cane et al., J. Mol. Spectrosc. 150 , 222–228 (1991)), and other ring-condensed aza-aromatic compounds although the relative amount of the type B and A components is different in each band. The transition moment is in the molecular plane nearly equidistant from the a - and b -inertial axes ( θ = ±42°).

The microwave spectrum of indazole and its ND isotopomer has been investigated at 70°C. The tautomer with the NH group closer to the phenyl ring is found to be the more stable both by the analysis of the rotational spectrum and ab initio calculations. The second tautomer is calculated at HF/4–21G level of theory to be 2800 cm−1 higher in energy. Information on the dipole moment and the low energy vibrational excited states has also been obtained.

The microwave spectra of benzimidazole and of its N-D monodeuterated isotopic species, obtained at 120°C, show the full planarity of the molecule. Information on the lower energy vibrational excited states, and on the dipole moment have also been obtained.

The 000 band of the 283-nm system of 4-azabenzimidazole has been analyzed by computer simulation of its rotational contour to establish the character of the S1-S0 electronic transition. The 000 band has been shown to be an A B hybrid with an intensity ratio B A = 0.15 , so the S1-S0 system can be assigned as A 1 A′(π ∗ -π)- X 1 A′ . Since the 000 band of the 289-nm system for 7-azaindole has also been shown to be of the same type (K. H. Hassan and J. M. Hollas, J. Mol. Spectrosc. 138, 398–412 (1989)), we conclude that the addition of an extra nitrogen in 4-azabenzimidazole does not change the nature of the first singlet electronic transition.

Perchloryl fluoride, FClO(3), has been studied both experimentally and theoretically, using high-resolution Fourier transform spectroscopy and high-level ab initio methods. The geometry, dipole moment, and anharmonic force field of the molecule have been calculated ab initio, using the coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] level of theory. The infrared spectra of monoisotopic species have been recorded. The nu(1) + nu(2) bands 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), the nu(2) + nu(3) and nu(2) + nu(3) - nu(3) bands of F(35)Cl(16)O(3) and F(37)Cl(16)O(3), and the 2nu(3) - nu(3) band of F(37)Cl(16)O(3) have been analyzed. The spectroscopic parameters obtained from these and from previous analyses have been compared with the theoretical results.

The global analysis of published high-resolution vibration-rotation spectra of (C2HD)-C-12 in the bending spectral range is presented, resulting in an extension of the known vibration-rotation assignments, including a new band 2v(4)+v(5)