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°.     

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.     

Rotational spectrum of sulfuryl bromide fluoride

The rotational spectra of SO₂⁷⁹BrF and SO₂⁸¹BrF have been obtained between 18 and 40 GHz. Both molecules are near-prolate symmetric rotors with a and b-type dipole components. A least-squares fit of the observed moments of inertia obtained by correcting for the bromine quadrupole interaction yields $\text{r}\text{(SBr) = 2.155 ± 0.006}\text{A}\text{?}$ and ? FSBr=100.6°±1.5° structural parameters when $\text{r}\text{(SO) = 1.407}\text{A}\text{?}$, $\text{r}\text{(SF) = 1.56}\text{A}\text{?}$, and ? OSO=123.7° are assumed.     

Ground state spectroscopic constants of H15NCS,HN13CS,and HNC34S,and the molecular structure of isothiocyanic acid

The rotational spectrum of isothiocyanic acid was measured for the isotopically enriched species H¹⁵NCS and HN¹³CS as well as HNC³⁴S in natural abundance. In the frequency range from 8 to 240 GHz the a-type R-branch transitions were measured for all three isotopic species. The ^qQ₁ transitions were identified in the microwave region for H¹⁵NCS and HN¹³CS. The rotational and centrifugal distortion constants were determined using Watson's Hamiltonian in the S reduction, extended empirically to higher order terms in the angular momentum. The molecular structure of isothiocyanic acid was reevaluated using a modified substitution method and the NCS chain was found to be bent: $\text{r(}\text{NH}\text{) = 0.993}\text{A}\text{?}$, $\text{r(}\text{NC}\text{) = 1.207}\text{A}\text{?}$, $\text{r(}\text{CS}\text{) = 1.5665}\text{A}\text{?}$, ∠HNC = 131.7°, and ∠NCS = 173.8°. The molecule has the trans conformation.     

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 $\text{r}{}_{\mathrm{e}}\text{(}\text{CO}\text{) = 1.1756 ± 0.0032}\text{A}\text{?}$, $\text{r}{}_{\mathrm{e}}\text{(}\text{CCl}\text{) = 1.7381 ± 0.0019}\text{A}\text{?}$.     

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.     

Microwave l-type resonance transitions of the v6 = 1 state in CHF3 and CDF3: Accidental degeneracy and molecular structure

Observations of the direct l-type resonance transitions in the microwave spectrum of the v₆ = 1 state of CHF₃ and CDF₃ have been extended to J = 37. Accidental degeneracies were found between J = 34, $\text{K}\text{= 3}\text{and}\text{0}$ in both molecules enabling the C rotational constants of CHF₃ and CDF₃ to be determined, using 118 observed frequencies for CHF₃ and 104 for CDF₃. After suitable correction the B and C rotational constants were used to determine the r₀, r₂, and r_e structures for CHF₃ and CDF₃.The equilibrium structure was determined to be $\text{CH}\text{= 1.091 ± 0.014}\text{A}\text{?}$, $\text{CF}\text{= 1.3284 ± 0.0031}\text{A}\text{?}$ and ∠FCF = 108.58 ± 0.34°.     

Doppler-limited dye laser excitation spectroscopy of the DSO radical

The $\text{A}\text{?}{}^2\text{A′(003) ←}\text{X}\text{?}{}^2\text{A″(000)}$ vibronic transition (16 370 to 16 425 cm^?1) of the DSO radical in studied by Doppler-limited dye laser excitation spectroscopy. DSO is produced in a flow system by reacting the products of a microwave discharge in O₂ with D₂S. About 637 observed lines are assigned to 987 transitions of the 19 subbands: K′_a ← K″_a = 6 ← 5, 5 ← 4, 4 ← 3, 3 ← 2, 2 ← 1, 1 ← 0, 0 ← 1, 1 ← 2, 2 ← 3, 3 ← 4, 0 ← 0, 1 ← 1, 2 ← 2, 3 ← 3, 4 ← 4, 3 ← 1, 2 ← 0, 0 ← 2, and 1 ← 3. They are analyzed to determine rotational constants, centrifugal distortion constants, and spin-rotation constants for both the ground and the excited electronic states. The band origin obtained is 16 413.874 (2.5σ = 0.002) cm^?1. The rotational constants determined are combined with the previous result on HSO (M. Kakimoto et al., J. Mol. Spectrosc.80, 334–350 (1980)) to calculate the structural parameters for this radical in both the states: $\text{r(}\text{SO}\text{) = 1.494(5)}\text{A}\text{?}$, $\text{r(}\text{SH}\text{) = 1.389(5)}\text{A}\text{?}$, and ∠HSO = 106.6(5)° for the $\text{X}\text{?}{}^2\text{A″}$ state, and $\text{r(}\text{SO}\text{) = 1.661(10)}\text{A}\text{?}$, $\text{r(}\text{SH}\text{) = 1.342(8)}\text{A}\text{?}$, and ∠HSO = 95.7(21)° for the $\text{A}\text{?}{}^2\text{A′(003)}$ state, where values in parentheses denote 2.5σ.     

Structure of dichlorine monoxide as studied by microwave spectroscopy. Determination of equilibrium structure by a modified mass dependence method

The microwave spectra of four isotopic species of dichlorine monoxide (OCl₂) have been observed, and the rotational constants have been obtained. The r_m structure for each isotopic species has been determined by Watson's method. The equilibrium structure has been estimated by taking proper averages of r_m structures to be $\text{r}{}_{\mathrm{e}}\text{(OCl) = 1.69587(7)}\text{A}\text{?}$ and ∠_eClOCl = 110.886(6)°. The general applicability and the merit of the present method for estimating the equilibrium structure are pointed out.     

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.     

The EPR and LMR spectra of the DO2 radical: Determination of ground-state parameters

The detection of lines in both the gas phase EPR spectrum at 9 GHz and the far-infrared LMR spectrum of the DO₂ radical is reported. The measurements are fitted with an appropriate Hamiltonian and several parameters for the molecule in the $\text{X}\text{?}{}^2\text{A″}$ state are determined. The majority of the transitions in the EPR spectrum are K-type doubling transitions and involve the a-component of the electric dipole moment. However the observation of one b-type transition (5₀₅-4₁₄) permits the determination of the off-diagonal component of the spin-rotation tensor, ?_ab, and an estimate of the relative magnitudes of the a- and b-components of the dipole moment. A combination of the parameters for HO₂ with those for DO₂ leads to a better understanding of the properties of the molecule. In particular, the r₀ molecular geometry has been determined more reliably than previously to be $\text{r}{}_0\text{(OH) = 0.9774}\text{A}\text{?}$, $\text{r}{}_0\text{(OO) = 1.3339}\text{A}\text{?}$, ∠HOO = 104.15°.     

Microwave spectrum of fluorodihydroxy borane,BF(OH)2

Fluorohydroxy borane, BF(OH)₂, has been identified in the hydrolysis of trifluoroborane by microwave spectroscopy. The rotational and centrifugal distortion constants have been determined for the normal and d₂ species. From these constants the molecular structure has been determined. This molecule does not have C₂ symmetry and the structural parameters are $\text{r}\text{(BO}{}_1\text{) = 1.360}\text{A}\text{?}$, $\text{r}\text{(BO}{}_2\text{) = 1.365}\text{A}\text{?}$, ∠FBO₁ = 118.2°, and ∠FBO₂ = 121.0°. The inertia defects establish the planarity of the molecule. The dipole moment of 1.818 ± 0.007 D has been obtained from the measurements of the Stark effects.     

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.     

The harmonic force field and rz structure of HNCO

The presently available microwave, millimeter wave, and far-infrared data of five isotopic species of isocyanic acid, namely, HNCO, H¹⁵NCO, HN¹³CO, HNC¹⁸O, and DNCO, have been used to obtain improved values of the ground-state rotational constants, the five quartic distortion constants, and some higher-order distortion constants in the I^rS reduced Hamiltonian of Watson. The appropriate planarity relation among the quartic centrifugal distortion constants has been imposed in the fitting procedure. The general harmonic force field of isocyanic acid has been determined using all existing data, and assuming a trans bent equilibrium geometry of the molecule with an NCO angle of 170°. Finally an r_z structure has been obtained using the A_z, B_z, and C_z rotational constants of five isotopic species. The bending of the NCO chain is found to be 8° in the trans configuration.     

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.     

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.     

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.     

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 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.