Internal rotation and molecular structure of ethaneselenol by microwave spectroscopy

The microwave spectra of ethaneselenol and its deuterated and ¹³C-substituted species were measured and assigned for the gauche and trans isomers. The double minimum splittings in the gauche isomers were directly observed for the species having a symmetry plane in the frame part. The rotational constants and the torsional splitting of the gauche isomer of the parent species were determined to be A = 27 148.86 ± 0.05, B = 3 623.68 ± 0.01, C = 3 399.21 ± 0.03, and Δν = 1 083.33 ± 0.04 MHz. From the torsional splittings of the parent and SeD species together with the vibrational frequencies already reported by Durig and Bucy, the Fourier coefficients of the selenol internal rotation potential function were determined to be V₁ = ?44 ± 17, V₂ = ?260 ± 3, V₃ = 1202 ± 16, and V₆ = ?43 ± 9 cal/mole. From the rotational constants obtained, the r_s structural parameters of the gauche and trans isomers were determined. The structural parameters in the skeletal part for the gauche isomer are $\text{r}\text{(CC) = 1.524}\text{A}\text{?}$, $\text{r}\text{(CSe) = 1.957}\text{A}\text{?}$, $\text{r}\text{(SeH) = 1.467}\text{A}\text{?}$, α(CCSe) = 113°31′, α(CSeH) = 93°05′, and the dihedral angle τ(CCSeH) = 61°39′. Those for the trans isomer are $\text{r}\text{(CC) = 1.525}\text{A}\text{?}$, $\text{r}\text{(CSe) = 1.962}\text{A}\text{?}$, $\text{r}\text{(SeH) = 1.440}\text{A}\text{?}$, α(CCSe) = 108°43′, and α(CSeH) = 93°30′. These parameters were compared with the corresponding ones of ethanethiol.     

The microwave spectrum,structure, and dipole moment of cis-1,2,3-trifluorocyclopropane

The microwave spectrum of cis-1,2,3-triflurocyclopropane has been investigated in the region 8–40 GHz. A fit of the oblate symmetric top spectrum gives a rotational constant of 4064.925 ± 0.022 MHz. A molecular structure was determined using the rotational constants obtained from assignments of the monodeutero species and the carbon-13 species. The molecular parameters are $\text{r}\text{(CH) = 1.095 ± 0.002}\text{A}\text{?}$, $\text{r}\text{(CC) = 1.507 ± 0.001}\text{A}\text{?}$, $\text{r}\text{(CF) = 1.354 ± 0.001}\text{A}\text{?}$ and ∠(HCF) = 112.3 ± 0.2°. The dipole moment was determined to be 3.89 ± 0.02 D. The structural parameters are compared to other substituted cyclopropyl ring structures and to molecular orbital predictions as well as to related fluorocarbons. The molecule provides another example of the effect of fluorine substitutions on shortening adjacent bonds. It is also found that nonbonded F?F distances tend to be constant.     

Determination of A0 for CH335Cl and CH337Cl from the ν4 infrared and Raman bands

The ν₄ infrared and Raman bands of CH₃Cl were analyzed simultaneously. A direct fit yielded a complete set of constants for CH₃³⁵Cl, including A₀ = 5.20530 ± 0.00010 cm^?1 and D_K = (8.85 ± 0.13) × 10^?5cm^?1. For CH₃³⁷Cl an incomplete set of constants was obtained from the infrared band, and A₀ = 5.2182 ± 0.0010 cm^?1 was estimated by curve fitting of the Raman spectrum. The resulting equilibrium structure is $\text{r(}\text{CH) = 1.0854 ± 0.0005}\text{A}\text{?}$, $\text{r(}\text{CCl) = 1.7760 ± 0.0003}\text{A}\text{?}$, and <(HCH) = 110°.35 ± 0°.05.     

Microwave spectra of deuterated ethylenes: Dipole moment and rz structure

The pure rotational spectra of three deuterated ethylenes, CH₂CD₂, CH₂CHD, and cis-CHDCHD, were observed by microwave spectroscopy, and the rotational and centrifugal distortion constants were determined precisely. The dipole moment of CH₂CD₂ was calculated from the Stark effects to be 0.0091 ± 0.0004 D. From the observed rotational constants the average structure was calculated to be $\text{r}{}_{\mathrm{z}}\text{(CC)}\text{= 1.3391 ± 0.0013}\text{A}\text{?}$, $\text{r}{}_{\mathrm{z}}\text{(CH)}\text{= 1.0869 ± 0.0013}\text{A}\text{?}$, θ_z(CCH) = 121.28 ± 0.10°, and $\text{r}{}_{\mathrm{z}}\text{(CH)}\text{- r}{}_{\mathrm{z}}\text{(CD)}\text{= 0.00137 ± 0.00037}\text{A}\text{?}$, where the errors include one standard deviation in the fitting and errors due to an uncertainty (±0.03°) in θ_z(CCH) - θ_z(CCD).     

Microwave spectrum of dimethyldichlorosilane

The microwave spectrum of dimethyldichlorosilane has been observed and the rotational constants and centrifugal distortion constants have been determined for ³⁵Cl₂ and ³⁵Cl³⁷Cl species. From these constants, the molecular structure is determined as $\text{r(}\text{SiCl}\text{) = 2.055 ± 0.003}\text{A}\text{?}$, $\text{r(}\text{SiC}\text{) = 1.845 ± 0.005}\text{A}\text{?}$, ∠ClSiCl = 107.2 ± 0.3°, ∠CSiC = 114.7 ± 0.3°. An analysis of the ³⁵Cl₂ quadrupole splittings leads to quadrupole coupling constants of χ_aa = ?19.6 ± 0.3 MHz, χ_bb = ?3.7 ± 1.4 MHz, χ_cc = 23.3 ± 1.4 MHz, χ_bond = ?38.0 ± 1.6 MHz, and η_bond = 0.22 ± 0.08.     

Molecular structure of phosgene as studied by gas electron diffraction and microwave spectroscopy: The rz structure and isotope effect

The r_z structure of phosgene has been determined by a joint analysis of the electron diffraction intensity and the rotational constants as follows: $\text{r}{}_{\mathrm{z}}\text{(}\text{CO}\text{) = 1.1785 ± 0.0026}\text{A}\text{?}$, $\text{r}{}_{\mathrm{z}}\text{(}\text{CCl}\text{) = 1.7424 ± 0.0013}\text{A}\text{?}$, ∠_z;ClCCl = 111.83 ± 0.11°, where uncertainties represent estimated limits of experimental error. The effective constants representing bond-stretching anharmonicity have been obtained from an analysis of the isotopic differences in the r_z structure: $\text{a}{}_3\text{(}\text{CO}\text{) = 2.9 ± 0.9}\text{A}\text{?}{}^{\mathrm{?1}}$, $\text{a}{}_3\text{(}\text{CCl}\text{) = 1.6 ± 0.4}\text{A}\text{?}{}^{\mathrm{?1}}$. The equilibrium bond distances have been estimated from the r_z structure for the normal species and from the anharmonic constants to be $\text{r}{}_{\mathrm{e}}\text{(}\text{CO}\text{) = 1.1756 ± 0.0032}\text{A}\text{?}$, $\text{r}{}_{\mathrm{e}}\text{(}\text{CCl}\text{) = 1.7381 ± 0.0019}\text{A}\text{?}$.     

Further study of the microwave spectrum of chlorine lsocyanate: The substitution structure and nuclear quadrupole coupling

The microwave spectra of three further isotopic species of chlorine isocyanate (³⁵Cl¹⁵N¹²C¹⁶O, ³⁷Cl¹⁵N¹²C¹⁶O, ³⁵Cl¹⁴N¹³C¹⁶O) have been measured. From them we have obtained rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants. The data are combined with earlier data (1) to confirm the planarity of the molecule, and to give a full substitution structure as follows: $\text{r}\text{(ClN) = 1.705 ± 0.005}\text{A}\text{?}$; $\text{r}\text{(NC) = 1.226 ± 0.005}\text{A}\text{?}$; $\text{r}\text{(CO) = 1.162 ± 0.005}\text{A}\text{?}$; < (ClNC) = 118°50′ ± 30′; < (NCO) = 170°52′ ± 30′, with Cl and O trans. We have also calculated the chlorine and nitrogen quadrupole coupling constants using the SCF-MO-CNDO method, and have obtained good agreement with the measured values. Evidence for in-plane π-bonding at nitrogen has been obtained.     

Molecular structure of phosgene as studied by gas electron diffraction and microwave spectroscopy: The rs,rm, and re structures

The microwave spectra of eight isotopic species of COCl₂ have been observed, and the following rotational constants have been obtained: An analysis of the rotational constants has resulted in the r_s and r_m structures. The equilibrium structure, r_e, has been estimated by combining the r_m parameters derived according to Watson's method and the r_e bond distances estimated in our recent electron-diffraction and spectroscopic studies to be $\text{r}{}_{\mathrm{e}}\text{(CO}\text{) = 1.1756 ± 0.0023}\text{A}\text{?}$, $\text{r}{}_{\mathrm{e}}\text{(CCl}\text{) = 1.7381 ± 0.0019}\text{A}\text{?}$, ∠_eClCCl = 111.79 ± 0.24°.     

Molecular structure and centrifugal distortion constants of isocyanic acid from the microwave,millimeter wave,and far-infrared spectra

The pure rotational spectra of HNCO and DNCO were measured in the far-infrared region from 80 to 350 cm^?1 by a Fourier transform spectrometer with a resolution of 0.1 cm^?1. The ^rR_K branches were measured and assigned for HNCO from K = 1 to 6, and for DNCO from K = 3 to 8. The measured transition wavenumbers were analyzed together with the microwave and millimeter wave data reported by Hocking, Gerry, and Winnewisser [Can. J. Phys.53, 1869–1901 (1975)] and with the far-infrared data of Krakow, Lord, and Neely [J. Mol. Spectrosc.27, 148–176 (1968)] in the low-wavenumber region. The microwave and millimeter wave data of H¹⁵NCO, HN¹³CO, and HNC¹⁸O reported by Hocking et al. were reanalyzed assuming several centrifugal distortion constants to be identical with those of the normal species. The molecular structure of HNCO was reevaluated using a modified substitution method from the rotational constants obtained in this work. The molecule has a bent structure in a trans configuration with $\text{r}\text{(NH) = 0.995}\text{A}\text{?}$, $\text{r}\text{(NC) = 1.314}\text{A}\text{?}$, $\text{r}\text{(CO) = 1.668}\text{A}\text{?}$, ∠HNC = 123.9°, and ∠NCO = 172.6°.     

The microwave spectrum,structure, and quadrupole coupling constants of boron chloride difluoride,BCIF2

The microwave spectrum of boron chloride difluoride, BClF₂, has been investigated in the region 26.5–40.0 GHz. R-branch transitions belonging to the isotopic species ¹¹B³⁵Cl¹⁹F₂, ¹¹B³⁷Cl¹⁹F₂, and ¹⁰B³⁵Cl¹⁹F₂ have been observed and the derived rotational constants yield the following ground-state structural parameters: $\text{r}{}^0\text{(BF) = 1.315 ± 0.006}\text{A}\text{?}$, $\text{r}{}^{\mathrm{s}}\text{(BCl) = 1.728 ± 0.009}\text{A}\text{?}$, < FBF = 118.1 ± 0.5°. The ground-state rotational constants of the most abundant species ¹¹B³⁵Cl¹⁹F₂ are: A₀ = 10 449.32 ± 0.13, B₀ = 4705.811 ± 0.020, C₀ = 3239.702 ± 0.026 MHz, Δ_JK = 8.9 ± 1.7, and Δ_J = 1.86 ± 0.48 KHz. The asymmetry parameter κ = ?0.593291 and the inertial defect δ⁰ = 0.2361 amu Ų which is consistent with that expected for this type of molecule if planar. The ³⁵Cl quadrupole coupling constants for ¹¹B³⁵Cl¹⁹F₂ are χ_aa = ?42.8 ± 1.0, χ_bb = 30.2 ± 1.5, χ_cc = 12.6 ± 1.5 MHz with the asymmetry parameter η = 0.41.     

Microwave spectrum and structure of cyanamide: Semirigid bender treatment

An extensive study of the microwave spectrum of cyanamide has been undertaken, the analysis being based in part on semirigidbender calculations by the methods of Bunker and Szalay. Inversion lines of NH₂CN, $\text{K}{}_{\mathrm{?1}}\text{= 2}{}^{\mathrm{a}}\text{Q}$ branches and a number of vibrational satellites of the J = 2?1 transition were observed. A two-vibrational-state Hamiltonian was used to fit simultaneously the 0⁺ and 0^? microwave data and yielded rotational constants X, Y, Z, D_J, D_JK, d₁, H_JK as well as the inversion splitting and the μ_yz-connecting matrix element. Vibrational satellite data of seven isotopic species and infrared frequencies of NH₂CN were included in the semirigid bender calculations: The NCN spine is nonlinear by ca. 5° in the equilibrium structure of the molecule. Also, $\text{r}{}_{\mathrm{<mtext>NH</mtext>}}\text{A}\text{?}\text{= 0.9994 + 0.0144?}{}^2$; <HNH/2 = 60.39° ? 0.1134?²; $\text{r}{}_{\mathrm{<mtext>NC</mtext>}}\text{A}\text{?}\text{= 1.3301 + 0.0327?}{}^2$ (? is the inversion angle in rad); $\text{r}{}_{\mathrm{<mtext>CN</mtext>}}\text{= 1.1645}\text{A}\text{?}$ fixed. The inclusion of the NC bond flexing was necessary in order to reproduce the observed vibrational satellite patterns of NH₂CN, NHDCN, and ND₂CN. The barrier to inversion of the amino group is 510 ± 6 cm^?1 with minima at ±45.0 ±0.2°. The inversion dipole moment is 0.91 ± 0.02 Debye.     

Microwave spectrum of 2-propene-1-imine,CH2CHCHNH

The reactive species, 2-propene-1-imine, has been identified by its microwave spectrum as a pyrolysis product of diallylamine vapor (100 mTorr, 400°C). Two entirely planar forms are observed, both with an “s-trans” CCCN configuration. The lower energy rotamer has an “anti” CCNH configuration, with $\text{r}\text{CC = 1.453(3)}\text{A}\text{?}$, $\text{r}\text{CC = 1.336(4)}\text{A}\text{?}$, and ∠ CCC = 122.9(3)° and a dipole moment of 2.01(2) D with 1.13(1) D and 1.66(2) D “a” and “b” components. The higher energy rotamer has a “syn” CCNH configuration and a dipole moment of 2.51(2) D with 2.39(2) and 0.77(3) D the “a” and “b” components. From relative intensity measurements, the ground state energy difference is determined to be 0.9 ± 0.1 kcal mole^?1.     

The microwave spectrum,substitution structure,and dipole moment of thioketen,H2CCS

The microwave spectrum of the unstable thiocarbonyl thioketen, H₂CCS, has been investigated in the region 26.5–40 GHz. All singly substituted species as well as D₂CCS have been studied and the derived rotational constants yield the following structural parameters: $\text{r}{}_{\mathrm{<mtext>s</mtext>}}\text{(CS) = 1.554 ± 0.003}\text{A}\text{?}$, $\text{r}{}_{\mathrm{<mtext>s</mtext>}}\text{(CC) = 1.314 ± 0.003}\text{A}\text{?}$, $\text{r}{}_{\mathrm{<mtext>s</mtext>}}\text{(CH) = 1.090 ± 0.006}\text{A}\text{?}$, ∠_s(HCH) = 120.3 ± 0.5°. The dipole moment is μ = 1.02 ± 0.01 D. Four low frequency vibrational modes have been observed and their assignments are discussed.     

Force constant calculations of NCl3 and PCl3

A method based on the least-squares fitting of the observed vibrational frequencies, centrifugal distortion constants, mean-square amplitudes, and vibration-rotation interaction constants with respect to the harmonic force constants has been employed to determine the harmonic force field of NCl₃ and PCl₃. The results are compared with those obtained by other authors. An improved structure of PCl₃ has also been determined by analysis of the microwave spectrum of the P³⁷Cl₃ and P³⁵Cl₂³⁷Cl isotopic species. Two structures have been obtained with the following values of the parameters

$\text{r}{}_{\mathrm{s}}\text{(PCl)=2.0450±0.0072}\text{A}\text{?}\text{Cl}\text{P}\text{Cl=100°12′±20′}$

$\text{r}{}_{\mathrm{s}}\text{(PCl)=2.0426±0.0005}\text{A}\text{?}\text{Cl}\text{P}\text{Cl=100°6′±1′}$

     

Microwave spectrum of sulfur difluoride in the first excited vibrational states vibrational potential function and equilibrium structure

Microwave spectra of SF₂ in the first excited states of the three normal modes were observed and analyzed. A comparison of the observed inertia defects in the ν₁ and ν₃ states with those calculated by omitting the contributions of the Coriolis interaction between the two modes led to a $\text{ν}\text{?}{}_1\text{-}\text{ν}\text{?}{}_3$ vibrational frequency differences of 25.72 ± 0.33 cm^?1, with ν₁ being definitely higher. The inertia defect in the ground state and our measured values for the inertia defect in the ν₂ state and for the $\text{ν}\text{?}{}_1\text{-}\text{ν}\text{?}{}_3$ difference were combined with the centrifugal distortion constants of Kirchhoff et al. [J. Mol. Spectrosc.48, 157–164 (1973)] to improve the harmonic force field. The interaction constant between the two SF stretching coordinates was determined precisely. The third-order and the cubic anharmonic potential constants were calculated from the observed vibration-rotation constants. The equilibrium structure was determined to be $\text{r}{}_{\mathrm{e}}\text{(}\text{SF}\text{) = 1.58745 ± 0.00012}\text{A}\text{?}$ and θ_e(FSF) = 98.048 ± 0.013°.     

The microwave spectrum of 1-phosphapropyne,CH3CP: Molecular structure,dipole moment,and vibration-rotation analysis

The J = 4 ← 3 and J = 3 ← 2 rotational transitions of 1-phosphapropyne, CH₃CP, between 26.5 and 40 GHz have been studied by microwave spectroscopy. The spectrum shows the characteristic vibration-rotation satellite patterns associated with a C_3v symmetric rotor. Apart from the most abundant isotope variant, the species ¹²CD₃¹²C³¹P, ¹²CD₂H¹²C³¹P, ¹²CH₂D¹²C³¹P, ¹³CH₃¹²C³¹P, ¹²CH₃¹³C³¹P, ¹³CD₃¹²C³¹P, and ¹²CD₃¹³C³¹P have also been studied. For ¹²CH₃¹²C³¹P the rotational constants B₀ = 4991.339 ± 0.003 MHz, D_J = 0.823 ± 0.092 kHz, D_JK = 66.59 ± 0.18 kHz have been determined. From these data the following structural parameters have been derived: $\text{r}{}_{\mathrm{s}}\text{(}\text{CH}\text{) = 1.107 ± 0.001}\text{A}\text{?}$, ∠_s(HCC) = 110.30 ± 0.09°, $\text{r}{}_{\mathrm{s}}\text{(}\text{CC}\text{) = 1.465 ± 0.003}\text{A}\text{?}$, $\text{r}{}_0\text{(}\text{CP}\text{) = 1.544 ± 0.004}\text{A}\text{?}$. The dipole moment has been determined as 1.499 ± 0.001 D by analysis of the Stark effect of the J = 3 ← 2, |K| = 1 line. The vibrational satellites (v_s = 1, 2, and 3) have been studied and various vibration-rotation parameters derived.     

Microwave spectrum,structure, dipole moment,quadrupole coupling constant,and internal motion of thioformamide

The r_s structure of thioformamide has been determined from the microwave spectra of the normal as well as isotopic species of the molecule. The structural parameters obtained assuming the planarity of the molecule are $\text{NH}{}_{\mathrm{c}}\text{= 1.001}{}_8\text{± 0.006}\text{A}\text{?}\text{,}\text{NH}{}_{\mathrm{t}}\text{= 1.006}{}_5\text{± 0.003}\text{A}\text{?}\text{,}\text{CN}\text{= 1.358}{}_2\text{± 0.003}\text{A}\text{?}\text{,}\text{CS}\text{= 1.626}{}_2\text{± 0.002}\text{A}\text{?}\text{,}\text{CH}{}_{\mathrm{a}}\text{= 1.09}{}_6\text{± 0.08}\text{A}\text{?}\text{, ?}\text{H}{}_{\mathrm{c}}\text{NH}{}_{\mathrm{t}}\text{, = 121°42′ ± 40′, ?}\text{H}{}_{\mathrm{c}}\text{NC}\text{= 117°55′ ± 40′, ?}\text{H}{}_{\mathrm{t}}\text{NC}\text{= 120°22′ ± 30′, ?}\text{NCS}\text{= 125°16′ ± 15′ ?}\text{NCH}{}_{\mathrm{a}}\text{= 108°}{}_{\mathrm{5\prime }}\text{± 5°,}\text{and}\text{?}\text{SCH}{}_{\mathrm{a}}\text{= 126°}{}_{\mathrm{39\prime }}\text{± 5°}$.The dipole moment is calculated from the Stark effects of the three transitions to be μ_a = 3.99 ± 0.02 D, μ_b = 0.13 ± 0.25 D, and μ_total = 4.01 ± 0.03 D, where the c component is assumed to be zero.The quadrupole coupling constant of the ¹⁴N nucleus is estimated using the doublet splittings observed for six Q-branch transitions; χ_cc - χ_bb = ?5.39 ± 0.15 MHz and χ_aa = 2.9 ± 1.2 MHz.Two sets of vibrational satellites are observed and assigned to the first excited state of the amino wagging and the NCS bending vibrations, respectively. The relative intensity measurement gives the vibrational energies of 393±40 cm^?1 and 457 ± 50 cm^?1 for NH₂CHS and 293 ± 30 cm^?1 and 393 ± 40 cm^?1 for ND₂CHS. The amino wagging inversion vibration in the molecule is discussed in comparison with that in formamide. It is most probable that the thioformamide molecule is also planar without any potential hump to the amino inversion at the planar configuration.     

The microwave spectrum,substitution structure and dipole moment of cyanobutadiyne,HCCCCCN

Cyanobutadiyne (cyanodiacetylene), HCCCCCN, is sufficiently stable at low pressures to permit its rotational spectrum to be studied by microwave spectroscopy. The spectrum consists of a series of R-branch transitions typical of a linear molecule. The transitions with J = 9 to 14 which lie between 26.5 and 40.0 GHz have been measured for the vibrational ground state. Transitions have also been detected in natural abundance for all possible singly substituted ¹³C and ¹⁵N isotopic species. Deuteriated cyanobutadiyne, DCCCCCN, has also been synthesized and its ground state spectrum recorded. These measurements have enabled a complete substitution structure to be derived for the first time for a polyacetylene: r₈(HC_a) = 1.0569 ± 0.001, r₈(C_aC_b) = 1.2087 ± 0.001, r₈(C_bC_c) = 1.3623 ± 0.003, r₈(C_cC_d) = 1.2223 ± 0.004, r₈(C_dC_e) = 1.3636 ± 0.003, $\text{r}{}_8\text{(}\text{C}{}_{\mathrm{e}}\text{}\text{N}\text{) = 1.1606 ± 0.001}\text{A}\text{?}\text{(10}{}^{\mathrm{?10}}\text{m}\text{)}$. The spectroscopic parameters for the ground state are B₀ = 1331.3313 ± 0.001 MHz and D₀ = 0.0257 ± 0.002 KHz. The dipole moment, determined from the Stark effects of the J = 9 and 10 lines, is 4.33 ± 0.03 Debye.     

Microwave spectrum,centrifugal distortion,substitution structure,and dipole moment of sulfine,CH2SO

The microwave spectrum of the reactive species sulfine (CH₂SO) has been studied. Assignments of 86 transitions of the ground vibrational state normal isotopic species, with J up to 60, have allowed a thorough centrifugal distortion analysis. With planarity implied by the I_c-I_a-I_b value of 0.1333 amu $\text{A}\text{?}{}^2$, spectral assignments of seven other isotopic modifications have resulted in the following substitution bond lengths and angles: CH_syn = 1.085 Å, CH_anti = 1.077 Å, CS = 1.610 Å, SO = 1.469 Å, ?HCH = 121.86^°, ?SCH_syn = 122.51^°, ?SCH_anti = 115.63^°, and ?CSO = 122.51^°. From Stark effect measurements of the normal and d₂ species, the dipole moment has been determined to be 2.994 D, oriented 25.50° relative to the SO bond and 9.61° relative to the normal species “a” axis. At an initial pressure of 30 mTorr in a clean brass waveguide, the lifetime of sulfine at 25°C is ～30 min.     

Microwave spectral study of 2-fluorophenol: cis conformer

The microwave spectra of 2-fluorophenol and its deuterated species have been observed and analyzed in the frequency ranges 12.5–18.0 GHz (KU band) and 21.5–26.0 GHz (K band) in the ground vibrational state at room temperature. For the normal species, the radio frequency-microwave double resonance spectrum has been recorded in the frequency range 30.0–38.0 GHz. Three rotational and five quartic centrifugal distortion constants for the normal species, $\text{A}\text{?}\text{= 3337.86 ± 0.02}$, $\text{B}\text{?}\text{= 2231.92 ± 0.01}$, $\text{C}\text{?}\text{= 1337.52 ± 0.01}$, d_J = (3.5 ± 2.9) × 10^?4, d_JK = (?4.9 ± 1.5) × 10^?3, d_K = (?3.2 ± 1.0) × 10^?3, d_WJ = (?2.0 ± 1.0) × 10^?7, d_WK = (2.6 ± 0.8) × 10^?6 (in MHz), and three rotational constants for the deuterated species, $\text{A}\text{?}\text{= 3324.70 ± 0.03}$, $\text{B}\text{?}\text{= 2177.95 ± 0.03}$, $\text{C}\text{?}\text{= 1315.96 ± 0.03}$ (in MHz), have been obtained. Consideration of the r_s coordinate of the hydroxyl hydrogen atom leads to the assignment of the spectra to the cis conformer of the molecule. An r₀ structure for the cis conformer has been proposed. The nonbonded OH ? F distance is lower by about 0.3 Å than the sum of the van der Waals radii.