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The high resolution infrared spectrum of 14 ND 3 has been re-investigated in the intervals 450–1600 cm −1 and 2200–2800 cm −1 , where the absorption lines of the ν 2 /ν 4 /2ν 2 and ν 1 /ν 3 /2ν 4 band systems are located. The analysis of the bending fundamentals ν 2 and ν 4 has been extended assigning 844 transitions belonging to the 2ν 2 and 2ν 2 ←ν 2 cold and hot bands. In total, 3436 transitions, of which 3358 are vibration−rotation−inversion and 78 inversion transitions in the v 2 =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 v 2 =1, 2 and v 4 =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 ν 1 and ν 3 have been extended to higher J and K transitions. The number of transitions of ν 1 has been doubled and it has been increased by 23% for ν 3 . In addition, 805 transitions reaching the v 4 =2 0 and 2 ±2 s , a states have been identified. In total, 2408 transitions of the ν 1 /ν 3 /2ν 4 band system have been fitted simultaneously. The adopted effective Hamiltonian includes also the Fermi resonance terms between v 1 =1 and v 4 =2 0 and higher order Coriolis terms between v 1 =1/v 4 =2 ±2 , v 3 =1/v 4 =2 0 , and v 3 =1/v 4 =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. [ABSTRACT FROM AUTHOR]

[Display omitted] • 14ND 3 transitions are identified in the high resolution far and infrared spectra. • 816 rotation-inversion transitions in the ground state with J up to 31 are assigned. • 6408 transitions in the cold and hot bands to v 2 = 1,2 and v 4 = 1 are assigned. • 1357 rotation-inversion transitions in v 2 = 1,2 and v 4 = 1 are assigned and analyzed. • The model successfully reproduces the transitions at experimental accuracy. Ammonia is the object of extensive investigations due to the peculiar pattern of its interacting vibration states and its central role in astronomical sciences. 14ND 3 is of interest in astrochemistry because the determination of deuterium fractionation ratios in ammonia and its deuterated isotopologues contributes to a deeper knowledge of the chemistry in the cold, dense cores of the interstellar medium. Here, the ground, v 2 = 1, 2 and v 4 = 1, a , s states of 14ND 3 are analyzed thanks to new spectra recorded with the Canadian Light Source synchrotron, from 60 to 1500 cm−1 at a resolution ranging from 0.00096 to 0.003 cm−1. Overall, 7765 inversion, rotation-inversion, and vibration–rotation-inversion transitions in ν 2 , 2ν 2 , ν 4 , 2ν 2 ← ν 2 , 2ν 2 ← ν 4 , ν 4 ← ν 2 , ν 2 ← ν 2 , 2ν 2 ← 2ν 2 , and ν 4 ← ν 4 have been fitted simultaneously to characterize the s and a levels of the excited states. 4021 and 2388 transitions were assigned in the cold and hot bands, respectively, and 150 inversion and 1206 inversion-rotation transitions in v 2 = 1, 2 and v 4 = 1. 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 118 spectroscopic parameters, determined with high precision. In addition, a new analysis of the ground state has been performed. 9256 data have been fitted, 78 inversion and 837 rotation-inversion transitions, and 8341 ground state combination differences. An improved set of parameters and term values are derived thanks to the increased precision of the newly assigned rotation-inversion transitions with J / K values up to 31/30 and to the larger number of the ground state combination differences. [ABSTRACT FROM AUTHOR]

Abstract: The infrared spectrum of the ammonia isotopologue 15ND3 has been investigated by high resolution Fourier transform spectroscopy in the region from 450 to 1600cm−1. In total, 2217 transitions involving the (s) and (a) inversion–rotation–vibration levels have been identified and assigned to the ν2 and ν4 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, 0.00071cm−1, is about two times the estimated measurement precision. [Copyright &y& Elsevier]

Abstract: The 2ν1 (A1) Si−H stretching overtone band of HSiD3 has been recorded at a resolution of ca. 0.009cm−1 between 4200 and 4400cm−1. About 790 ro-vibration transitions of the H28SiD3 isotopologue have been assigned, with J′ 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 A1/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. [Copyright &y& Elsevier]

The high resolution infrared spectra of the mono isotopic species F35Cl16O3, F37Cl16O3, F35Cl18O3 and F37Cl18O3 have been analysed in the region of the ν1 + ν5 perpendicular combination band, from 1540 to 1680 cm−1. For all the isotopologues the ν1 + ν5 band is of medium intensity at the recording conditions. In total, about 2400, 2000, 2600 and 2700 transitions have been assigned for F35Cl16O3, F37Cl16O3, F35Cl18O3 and F37Cl18O3, respectively. The data for each band have been analysed on the basis of the usual Hamiltonian for a degenerate state of a molecule of C3v symmetry. In addition, two interaction terms have been considered active within the v1 = v5 = 1 state, with and selection rules. The ro-vibration parameters of the v1 = v5 = 1 states have been obtained, together with the band origins. Combining the ν1 + ν5 origins with those of the ν1 and ν5 fundamentals, the anharmonicity constant has been derived for the four molecules and compared to the corresponding value calculated ab initio. [ABSTRACT FROM PUBLISHER]

A high resolution Fourier transform infrared spectrum of C2H6, measured at a pressure of 173.3 Pa and an optical path of 153.2 m, was analysed between 1050 and 1295 cm−1. Extensive absorption due to the difference bands ν 11–ν 4, and several rotation–torsion lines of the difference band ν 2–ν 4, in the region of the x, y-Coriolis resonance of ν 2 and ν 11, were observed. This allowed a detailed rotation–torsion analysis of the upper states ν 11 and ν 2. The anomalous torsional structure, found in the non-degenerate vibrational state ν 2, can be explained as the effect of an Hamiltonian term accounting for a strong dependence of the torsional barrier height on the normal vibrational coordinate q 2. The value of the barrier height derivative is estimated to be 127 ± 10 cm−1. Also detected and assigned were ‘hot’ difference transitions belonging to the (ν 4 + ν 11)–2ν 4 band, yielding information on the upper state ν 4 + ν 11. It is believed that transitions from 3ν 4 to 2ν 4 + ν 11 are also detectable in the investigated region. [ABSTRACT FROM PUBLISHER]

The high-resolution infrared spectra of the mono isotopic species F35Cl16O3, F37Cl16O3, F35Cl18O3 and F37Cl18O3 have been analysed in the region of the ν 2 + ν 4 and 2ν 2 + ν 5 perpendicular combination bands, from 1920 to 2060 cm−1. Both bands are perturbed by the anharmonic interaction effective between the v 2 = v 4 = 1 and v 2 = 2, v 5 = 1 excited states of E symmetry. The ν 2 + ν 4 bands are of medium–strong intensity, while the 2ν 2 + ν 5 bands are very weak. Since the origins of the two bands differ by about 10 cm−1, the 2ν 2 + ν 5 bands at lower wavenumbers are almost completely hidden by ν 2 + ν 4. In total, about 3400, 2400, 2800 and 3200 transitions have been assigned for F35Cl16O3, F37Cl16O3, F35Cl18O3 and F37Cl18O3, respectively. The assignments of each dyad have been analysed simultaneously with the inclusion of the anharmonic resonance term in the model Hamiltonian. The ro-vibration parameters of the v 2 = v 4 = 1 and v 2 = 2, v 5 = 1 excited states have been obtained, together with the deperturbed band origins and the anharmonic resonance coefficients W 245. Combining the ν 2 + ν 4 origins with those of the ν 2 and ν 4 fundamentals, the anharmonicity constants x 24 have been derived for the four molecules and compared with the ab initio values calculated taking into account the Fermi resonance. [ABSTRACT FROM PUBLISHER]

Abstract: The Fourier transform infrared spectrum of ethane between 2860 and 3060cm−1 has been re-investigated under high resolution at 229K. The infrared absorption in this region is due mainly to the CH stretching fundamentals ν 5 (parallel band) and ν 7 (degenerate perpendicular band), and to the parallel combination system ν 8 + ν 11 (A 4s, A 3s). All the relevant perturbation mechanisms affecting the observed absorption patterns have been clarified. In particular, the main perturbers of the ν 7 state are identified to be the degenerate vibrational combination states ν 8 + ν 11 (l-type interaction) and ν 3 +2ν 4 + ν 8 (Fermi-type interaction). Because of the last interaction, the K″ΔK =−6 transitions occur with intensities comparable to both the infrared active fundamental ν 7 and the almost dark combination ν 3 +2ν 4 + ν 8. The parallel combination system ν 8 + ν 11 (A 4s, A 3s) is overlapped and heavily perturbed by the nearby parallel system ν 4 + ν 11 + ν 12 (A 4s, A 3s), whose K-structure is spread by the strong z-Coriolis interaction of its two vibrational components. In this work, 95 new transitions to the perturbers of ν 7 have been assigned. They belong mostly to the degenerate vibrational states ν 8 + ν 11 (E 1d) and ν 3 +2ν 4 + ν 8 (E 1d), and to the parallel system ν 8 + ν 11 (A 4s, A 3s). A least squares fit calculation, limited to the ν 7 degenerate fundamental and its degenerate perturbers ν 8 + ν 11, ν 3 +2ν 4 + ν 8, ν 4 + ν 11 + ν 12, and ν 3 +3ν 4 + ν 12 was performed. From the results of this fit, we created a line-by-line database containing the molecular parameters for 4969 transitions in these five bands of 12C2H6. Finally, we identified the degenerate combination band ν 2 + ν 8 (62 observed transitions) to be the main perturber (x, y-Coriolis-type interaction) of the parallel fundamental ν 5. [Copyright &y& Elsevier]

Abstract: High resolution infrared spectra of 121SbHD2 and 123SbHD2 have been studied in the region of , the Sb–H stretching fundamental, from 1780 to 1990cm−1. The stretching overtone band of 123SbHD2, located in the 3640–3790cm−1 range, has also been investigated. The SbHD2 molecule is an asymmetric rotor of Cs symmetry with the asymmetry parameter κ =0.61. The 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 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 transitions. In total, 3942 GSCD up to = 27, =25, and =20 have been fitted with σ =0.52×10−3 cm−1. Only C-type transitions have been observed in the weak overtone band. The 556 assigned transitions have been fitted with σ =2.6×10−3 cm−1 using the same Hamiltonian as for . In the band of 121SbHD2 771 C-type transitions have been assigned, and the 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 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. [Copyright &y& Elsevier]

Abstract: The high resolution infrared spectrum of the mono-isotopic species 123SbD3 has been studied in the regions of the first and second Sb–D stretching overtones, from 2600 to 2800cm−1 and from 3900 to 4100cm−1, respectively. In both regions only two almost degenerate bands of similar intensity have been observed, one parallel and the other perpendicular, corresponding to the low-lying states in the manifolds of the excited vibrational states. These bands have been identified as 2ν 1(A 1)/ν 1 + ν 3(E) in the first overtone and 3ν 1(A 1)/2ν 1 + ν 3(E) in the second overtone band system. About 1700 transitions with have been assigned to the 2ν 1(A 1)/ν 1 + ν 3(E) and about 700 with to the 3ν 1(A 1)/2ν1+ ν 3(E) dyad. The transitions assigned to each dyad have been fitted simultaneously since the A 1/E excited states are affected by strong Coriolis and k-type perturbations treated explicitly in the model. Eventually, the extent to which the parameters resulting from the analyses fulfill the local mode theory requirements has been evaluated. Differently from SbH3, the deuterated species does not reach true local mode behavior, even in the second overtone. [Copyright &y& Elsevier]

[Display omitted] • NH 2 D and ND 2 H transitions are identified in the high resolution far infrared spectra. • For NH 2 D, 2153 precise transitions in the ground state with J up to 24 are assigned. • For ND 2 H, 3214 precise transitions in the ground state with J up to 28 are assigned. • Watson-type S reduced Hamiltonian, representations IIIr and IIIl, was adopted. • The model successfully reproduces the transitions at experimental accuracy. Transitions of NH 2 D and ND 2 H have been detected in the high resolution spectrum of 14ND 3 recorded at unapodized resolution of 0.00096 cm−1 in the region 60–600 cm−1 using the Bruker IFS 125 Fourier transform spectrometer located at the synchrotron far-infrared beamline, Canadian Light Source. In this study we report on the observation and analysis of the spectrum for the ground state of NH 2 D and ND 2 H. 2153 rotation and rotation-inversion transitions, with J up to 24, were assigned for NH 2 D, and 3214 transitions, with J up to 28, for ND 2 H. The newly assigned transitions, together with those present in the literature, were fitted on the basis of a Watson-type S reduced Hamiltonian using the IIIr and IIIl representations for NH 2 D and ND 2 H, respectively. The model Hamiltonian includes terms up to the 10th power of the angular momentum and vibration–rotation interaction terms between the inversion states. Precise and extended sets of spectroscopic effective parameters were derived for both isotopologues as results of least squares weighted fit procedures that reproduce the transition wavenumbers at experimental accuracy. [ABSTRACT FROM AUTHOR]

Abstract: We report the global analysis of methane (12CH4) lines from high resolution rovibrational spectra including accurate line positions and intensities in the region 0–4800cm−1. This covers four polyads: The Ground State Monad (rotational levels), the Dyad (940–1850cm−1, 2 vibrational levels, 2 sublevels), the Pentad (2150–3350cm−1, 5 vibrational levels, 9 sublevels) and the Octad (3550–4800cm−1, 8 vibrational levels, 24 sublevels) and some of the associated hot bands (Pentad–Dyad and Octad–Dyad). New Fourier transform infrared (FTIR) spectra of the Pentad and Octad regions have been recorded with a very high resolution (better than 0.001 cm−1 instrumental bandwidth, unapodized) at 78K using the Bruker IFS 125 HR Zürich prototype (ZP2001) spectrometer in combination with a long optical path collisional cooling system [S. Albert, S. Bauerecker, M. Quack, A. Steinlin, Mol. Phys. 105 (2007) 541]. Existing spectra previously recorded with the FTIR spectrometer at the National Solar Observatory on Kitt Peak in Arizona were remeasured selectively to provide new intensities and positions of weaker lines above 4400cm−1. These were combined with previously reported absorption data from FTIR and laser absorption, as well as high-resolution stimulated Raman and microwave spectra. The effective hamiltonian was expanded up to order 6 for the Ground State, order 6 for the Dyad, order 5 for the Pentad and order 5 for the Octad. A total of 16,738 line positions were used in the least squares adjustment characterized by the following global root mean square deviations d RMS for line positions: 1.3×10−4 cm−1 for the Dyad, 6.0×10−4 cm−1 for the Pentad, and 3.5×10−3 cm−1 for the Octad. Absolute intensities were also analyzed for all the cold bands and some of the hot bands in the region under consideration and we obtained d RMS =9.6% including 3262 experimental line intensities for the Octad. This analysis represents a large improvement over the previous one [J.-C. Hilico, O. Robert, M. Loëte, S. Toumi, A.S. Pine, L.R. Brown, J. Mol. Spectrosc. 208 (2001) 1] with d RMS =0.041cm−1 for positions and 15.6% for intensities in the Octad for a smaller data set. The new results are discussed as benchmarks in relation to accurate potential energy hypersurfaces and for atmospheric and planetary spectra. [Copyright &y& Elsevier]

Abstract: High resolution Fourier transform spectra of a sample of sulfur dioxide, enriched in 34S (95.3%). were completely analyzed leading to a large set of assigned lines. The experimental levels derived from this set of transitions were fit to within their experimental uncertainties using Watson-type Hamiltonians. Precise band centers, rotational and centrifugal distortion constants were determined. The following band centers in cm−1 were obtained: ν 0(3ν 2)=1538.720198(11), ν 0(ν 1 + ν 3)=2475.828004(29), ν 0(ν 1 + ν 2 + ν 3)=2982.118600(20), ν 0(2ν 3)=2679.800919(35), and ν 0(2ν 1 + ν 3)=3598.773915(38). The rotational constants obtained in this work have been fit together with the rotational constants of lower-lying vibrational states [W.J. Lafferty, J.-M. Flaud, R.L. Sams, EL Hadjiabib, J. Mol. Spectrosc. 252 (2008) 72–76] to obtain equilibrium constants as well as vibration–rotation constants. These equilibrium constants have been fit together with those of 32S16O2 [J.-M. Flaud, W.J. Lafferty, J. Mol. Spectrosc. 16 (1993) 396–402] leading to an improved equilibrium structure. Finally the observed band centers have been fit to obtain anharmonic rotational constants. [Copyright &y& Elsevier]

Abstract: The room temperature spectrum of ethane in the region of the ν 6 and ν 8 fundamentals, between 1330 and 1610cm−1, has been re-investigated at a resolution of 0.002cm−1. It is shown that the complex spectral structure with numerous strong local perturbations, which had hindered a global analysis of this region until now, is caused by a network of l-type resonances acting within the Fermi (or torsional-Coriolis) coupled system ν 8, ν 4 + ν 12. The x,y-Coriolis interaction between ν 6 and ν 8 and vibration–rotation interactions between ν 6 and 2ν 4 + ν 9 also generate relevant effects on the spectrum. With an appropriate Hamiltonian model accounting for all these effects, we could fit 1814 upper state level energies belonging to ν 6, ν 8 and ν 4 + ν 12 with an overall RMS deviation better than 3.8×10−3 cm−1. The determined values of the intrinsic torsional splittings in the different vibrational states are in agreement with the theoretical expectations. The intrinsic torsional splitting almost vanishes in ν 8, as in digermane and disilane; it is slightly larger in ν 4 + ν 12 than in ν 4, due to the decrease of the torsional barrier height with the excitation of ν 12. For the 2ν 4 + ν 9 state, the determined values of the vibrational origin and torsional splittings are in good agreement with the large increase of the torsional barrier height expected with the excitation of the ν 9 mode. Several hot transitions originating from the v4 =1 torsional state have been observed. An analysis of 294 line positions belonging to the (ν 4 + ν 8)− ν 4 hot band has been performed, leading to a fit with a RMS deviation of 5.1×10−3 cm−1. It is shown that a complex network of l-type resonances is also active in the ν 4 + ν 8,2ν 4 + ν 12 system. [Copyright &y& Elsevier]

Abstract: The high resolution infrared spectra of monoisotopic F35Cl18O3 and F37Cl18O3 have been studied in the region of the ν 4 fundamentals, centered at 1278.3 and 1263.3cm−1, respectively. Large perturbations are observed in both bands due to a Fermi type anharmonic resonance with the ν 2 + ν 5 combination bands, centered at 1270.7cm−1 in F35Cl18O3 and 1257.3cm−1 in F37Cl18O3. In particular, they affect the kl >0 levels of the v 4 =1 and v 2 = v 5 =1 states which cross at kl ⩾18 in F35Cl18O3 and kl ⩾3 in F37Cl18O3, due to the opposite values of and . 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 ν 2 + ν 5. The rovibrational parameters and the interaction constants between the v 4 =1 and v 2 = v 5 =1 levels have been obtained. The depertubed band origins of ν 4 and ν 2 + ν 5 are 1277.310567(165) and 1271.753733(195)cm−1, respectively, and the anharmonic resonance constant is 2.804416(153)cm−1. For F37Cl18O3, 3022 transitions have been assigned, 38% belonging to the ν 2 + ν 5 combination band. The depertubed band origins are 1260.856338(123) and 1259.872338(134)cm−1, for ν 4and ν 2 + ν 5 and the constant is 2.9350669(405)cm−1. The equilibrium geometry of perchloryl fluoride, r e (ClO)=139.7(3)pm, r e (ClF)=161.0(5)pm, and α e (OClO)=115.7(4)degree, has been determined using the A e and B e equilibrium constants of the four symmetric isotopologues of perchloryl fluoride, F35/37Cl16O3 and F35/37Cl18O3. [Copyright &y& Elsevier]

Abstract: The ν 1(A1), Si–H stretching, ν 2(A1) and ν 4(E), Si–D stretchings, fundamental bands of HSiD3 have been recorded at an effective resolution of ca. 0.003cm−1 between 2080 and 2280cm−1 and between 1480 and 1720cm−1, respectively. Ro-vibrational transitions of the H28SiD3 isotopologue have been assigned in the two spectral ranges, about 700 belonging to ν 1, with J′ up to 25 and K up to 21, and about 1600 to the ν 2/ν 4 dyad, with J′ up to 24 and K′ up to 19. The spectra of all the bands evidence the existence of several perturbations. The transitions of ν 1 have been analyzed either neglecting or including in the model A1/E Coriolis-type interactions with nearby dark states. The υ 2 =1 and υ 4 =1 states have been fitted simultaneously taking into account several ro-vibrational interactions between them and, in addition, with the υ 5 =2, l =0 component, and with few other close dark states. The standard deviation of the fit for both ν 1 and the ν 2/ν 4 dyad is, however, more than one order of magnitude larger than the estimated experimental precision and is independent on the adopted model. [Copyright &y& Elsevier]

Abstract: The high resolution infrared spectrum of mono-isotopic F37Cl16O3 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 1292.15cm−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 0.00018cm−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 and . The anharmonic resonance constant cm−1 has been derived. The Δl =Δk =±2 and Δl =0, Δk =±3 essential resonances have been found to be effective in ν 4, while in ν 2 + ν 5 only the Δl =Δk =±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 F37Cl16O3 have been obtained. The standard deviation of the fit is 0.0006cm−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 F35Cl16O3 and F37Cl16O3. Using the A 0 and B 0 constants of all the symmetric species the r 0 geometry has also been derived. [Copyright &y& Elsevier]