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

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.     

Equilibrium structure and force field of nitrosyl chloride

The a-type rotational spectra of ¹⁶O¹⁵N³⁵Cl in the (100) excited vibrational state ($\text{ν}{}_1\text{? 1770}\text{cm}{}^{\mathrm{?1}}$) and of ¹⁸O¹⁵N³⁵Cl and ¹⁸O¹⁴N³⁷Cl in the ground state were observed. The equilibrium structure of nitrosyl chloride was calculated from the values of the equilibrium rotational constants B_e and C_e of the two isotopic species ¹⁶O¹⁴N³⁵Cl and ¹⁶O¹⁵N³⁵Cl. The ground-state rotational constants of seven isotopic species of nitrosyl chloride were used to calculate Watson's r_m structure, which was found to be in satisfactory agreement with the r_e structure. The quadratic and cubic force fields of nitrosyl chloride were simultaneously refined by optimizing the least-squares fit to a set of 48 experimental data which includes the sextic centrifugal distortion constants, with one quadratic and three cubic terms of the potential energy function constrained to the values computed by SCF/ab initio methods. All remaining quadratic and cubic SCF force constants were found to be in reasonably close agreement with the empirically determined constants.     

Excited vibrational state microwave spectra,structure, and force-field of trifluorosilane

The J = 2?1 microwave spectrum of six isotopic species of HSiF₃ has been observed and assigned in excited states of five of the six fundamental vibrations. The assignment is based on relative intensities, double resonance experiments, and trial anharmonic force constant calculations. Analysis of the spectra leads to experimental values for five of the $\text{α}{}_{\mathrm{r}}{}^{\mathrm{B}}$ constants, all three l-doubling constants q_t, one Fermi resonance constant φ₂₃₃, and one zeta constant $\text{ζ}{}_{\mathrm{6,\; 6}}{}^{\mathrm{(z)}}$.The harmonic force field has been refined to all the available data on vibration wavenumbers, centrifugal distortion constants, and zeta constants. The cubic anharmonic force field has been refined to the data on $\text{α}{}_{\mathrm{r}}{}^{\mathrm{B}}$ and q_t constants, using two models: a valence force model with two cubic force constants for SiH and SiF stretching, and a more sophisticated model. With the help of these calculations, the following equilibrium structure has been determined: $\text{r}{}_{\mathrm{e}}\text{(}\text{SiH}\text{) = 1.4468(±5)}\text{A}\text{?}$, $\text{r}{}_{\mathrm{e}}\text{(}\text{SiF}\text{) = 1.5624(±1)}\text{A}\text{?}$, ∠HSiF = 110.64(±3)°,     

Infrared bands of 12C2HD

The rotational structure of about 40 bands of ¹²C₂HD observed in the region 6000?600 cm^?1 has been measured and interpreted with the purpose of determining a comprehensive set of molecular constants for this isotopic variety of acetylene. Combining these data with the results for ¹²C₂H₂ and ¹²C₂D₂, a reevaluation of the equilibrium internuclear distances for the acetylene molecule has been made: $\text{r}{}_{\mathrm{e}}\text{(CH) = 1.06215 ± 17 × 10}{}^{\mathrm{?5}}\text{A}\text{?}$ and $\text{r}{}_{\mathrm{e}}\text{(CC) = 1.20257 ± 9 × 10}{}^{\mathrm{?5}}\text{A}\text{?}$ were obtained. This paper presents all the molecular constants derived in this study.     

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°.     

Microwave spectrum of the molecular oxygen in the excited vibrational state

The fine-structure spectra of ¹⁶O₂ in the first excited vibrational state have been observed at room temperature with a double-modulation spectrometer. The spectra of an isotopic species ¹⁶O¹⁸O in the ground state are also observed in natural isotopic abundance. Revised energy formulas, which are derived as a slight extension of Tinkham and Strandberg's treatment, are used in the analyses, and much more accurate equilibrium molecular constants are determined; λ′_e = 59 429.08 ± 0.11 MHz, μ_e = ?252.265 ± 0.011 MHz, B_e = 43 336.2 ± 1.5 MHz, and $\text{r}{}_{\mathrm{e}}\text{= 1.20748 ± 0.00005}\text{A}\text{?}$.     

The emission spectra of H35Cl+, H37Cl+, D35Cl+, and D37Cl+ in the region 2700–4100 Å

The $\text{A}{}^2\text{Σ}{}^{\mathrm{+}}\text{-X}{}^2\text{Π}$ emission spectrum of HCl⁺ has been measured and analyzed for four isotopic combinations. These analyses extend previous work and provide rotational constants for the v = 0–2 levels of the ground state and for the v = 0–9 levels of the excited state. RKR potentials have been determined for both states, although the upper state could not be fitted precisely to such a model. Calculated relative intensities based on these potentials demonstrated that the electronic transition moment must change rapidly with lower state vibrational quantum number. Although considerable caution should be exercised in applying the concept of equilibrium constants to the $\text{A}{}^2\text{Σ}{}^{\mathrm{+}}$ state, the following are the best estimates of these constants (in cm^?1) for the $\text{X}{}^2\text{Π}$ state of H³⁵Cl⁺: B_e = 9.9406, ω_e = 2673.7, A_e = ? 643.7, and $\text{r}{}_{\mathrm{e}}\text{= 1.315}\text{A}\text{?}$. For the $\text{A}{}^2\text{Σ}{}^{\mathrm{+}}$ state of H³⁵Cl: T_e = 28 628.08, B_e ～ 7.505, ω_e ～ 1606.5, and $\text{r}{}_{\mathrm{e}}\text{= 1.514}\text{A}\text{?}$.     

Determination of molecular constants of nitric oxide from (1-0), (2-0), (3-0) bands of the 15N16O and 15N18O isotopic species

The (1-0), (2-0), and (3-0) transitions of ¹⁵N¹⁶O and ¹⁵N¹⁸O are investigated. The wavenumbers of the rotation-vibration lines are reported for the overtone bands and the ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (1-0) subband. It is shown that in the data reduction it is advantageous to calculate first merged spectroscopic constants ignoring the Λ-type doubling. The vibrational constants ω_e, ω_ex_e, ω_ey_e and the vibrational dependence of the rotational constants are determined. The study of ¹⁵N¹⁸O allows the determination of the equilibrium values of the centrifugal distortion correction A_De to the spin-orbit constant and of the spin-rotation constant γ_e from the isotopic invariance of the ratios $\text{A}{}_{\mathrm{<mtext>De</mtext>}}\text{B}{}_{\mathrm{<mtext>e</mtext>}}$ and $\text{γ}{}_{\mathrm{<mtext>e</mtext>}}\text{B}{}_{\mathrm{<mtext>e</mtext>}}$. It is found that $\text{A}{}_{\mathrm{<mtext>De</mtext>}}\text{B}{}_{\mathrm{<mtext>e</mtext>}}\text{= (?3.9 ± 1.3) × 10}{}^{\mathrm{?6}}$ and $\text{γ}{}_{\mathrm{<mtext>e</mtext>}}\text{B}{}_{\mathrm{<mtext>e</mtext>}}\text{= (?4.00 ± 0.05) × 10}{}^{\mathrm{?3}}$.     

Diode laser spectroscopy of the CCl radical

Vibration-rotation transitions of the fundamental band have been observed for both C³⁵Cl and C³⁷Cl in the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ states by using an infrared diode laser spectrometer with Zeeman modulation. A few lines of the “hot” band (v = 2 ← 1) have also been recorded for C³⁵Cl. From an analysis of the observed spectra improved values were obtained for the vibrational harmonic frequency and anharmonicity constant, rotational constants, and Λ-doubling parameters. It was found necessary to take into account centrifugal distortion effects on the spin-orbit coupling constant A in the analysis, which gave $\text{(}\text{dA}\text{dr}\text{)}{}_{\mathrm{<mtext>e</mtext>}}\text{r}{}_{\mathrm{<mtext>e</mtext>}}$ to be ?176 ± 38 or ?125 ± 38 cm^?1, depending upon whether ²Σ^? or ²Σ⁺ states contribute more to the Λ-type doubling. The equilibrium internuclear distance r_e was calculated from the derived rotational constants to be 1.64506 ± 0.00016 Å.     

Structure of cyclobutanone

The microwave spectra of the ¹⁸O and the α,α,α′,α′-tetradeuterated isotopic species of cyclobutanone have been investigated. Structural parameters determined are $\text{r}{}_{\mathrm{<mtext>CO</mtext>}}\text{= 1.204 ± 0.006}\text{A}\text{?}$, , ∠ H_αCH_α = 109.2 ± 1° with the methylene group tilted toward the carbonyl group by 4.6 ± 0.8°.     

Methyl barrier to internal rotation and quadrupole coupling constants in S-methylchlorothioformate

Internal rotation A-E splittings have been observed in the ground state for both ³⁵Cl and ³⁷Cl isotopic species of S-methylchlorothioformate. The values $\text{V}{}_3\text{(}{}^{35}\text{Cl}\text{) = 893 ± 20}$ and $\text{V}{}_3\text{(}{}^{37}\text{Cl) = 890 ± 20 cal/mole}$ have been obtained. The anaalysis of the hyperfine structure gave $\text{χ}{}_{\mathrm{aa}}\text{(}{}^{35}\text{Cl}\text{) = ?49.2}$, $\text{χ}{}_{\mathrm{bb}}\text{(}{}^{35}\text{Cl}\text{) = 22.4}$ and $\text{χ}{}_{\mathrm{aa}}\text{(}{}^{37}\text{Cl}\text{) = ?39.0}$, $\text{χ}{}_{\mathrm{bb}}\text{(}{}^{37}\text{Cl) = 18.3 MHz}$. Only the syn-conformation of the methyl group with respect to the carbonyl group has been observed. A partial r₀ structure is given.     

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,structure, and nuclear quadrupole coupling of cis-1-chlorobutadiene-1,3

The microwave spectra of the two natural isotopic species of cis-1-chlorobutadiene-1,3, CH³⁵ClCHCHCH₂ and CH³⁷ClCHCHCH₂, together with all monosubstituted species with deuterium or ¹³C isotopes have been measured and assigned and the complete substitution structure has been determined. The spectral region investigated was between 18 and 40 GHz. The molecule was found to be planar and the following values were found for the principal parameters: r(CC)_chlorovinyl = 1.327(6), $\text{r(}\text{CC}\text{)}{}_{\mathrm{<mtext>vinyl</mtext>}}\text{= 1.343(2)}\text{A}\text{?}$, <(CCC)_chlorovinyl = 126.5(3)° and <(CCC)_vinyl = 123.0(7)°. The nuclear quadrupole coupling constants, χ_aa and χ_bb, for the parent molecule were calculated and further used to estimate the symmetry of the field gradient around the CCl bond. Force-field calculations were used to predict the centrifugal distortion constants and inertial defect of some isotopic species. Thermodynamic functions were calculated for cis- and trans-1-chlorobutadiene-1,3 and used to estimate the energy difference between them.     

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).     

Molecular force field and structure of water: Recent microwave results

Recently, microwave studies of the rotational spectra of water and its various isotopic species have been reported. These studies provide rotational constants and among others the quartic distortion constants, which depend on the quadratic part of the vibrational potential function. These data are collected and discussed, and the molecular force field and structure of water is considered in light of this recent microwave data. The quartic distortion data gives force constants which are very reasonable considering the difficulties in the distortion analysis of these light molecules, where as many as 22 parameters are being evaluated to fit the observed spectrum. The infrared and microwave data are combined within the theoretical framework of the small oscillations model and the results compare favorably with the true harmonic force field. The infrared and microwave valence bond force constants of H₂O are (mdyn/Å):

$\text{?}{}_{\mathrm{r}}\text{=7.746, ?}{}_{\mathrm{\theta }}\text{=0.700, ?}{}_{\mathrm{rr}}\text{=?0.093, ?}{}_{\mathrm{r\theta }}\text{=0.379}$

The results further confirm the usefulness of rotation-vibration data in the determination of force constans, and show that even for water with extremely large anharmonicity effects, a very representative force field can be obtained by combining ground state infrared and microwave data.Various molecular structures have been evaluated, and the average structures in the ground vibrational state for H₂O, D₂O and T₂O are found to be:

$\text{〈r〉}\text{〈θ}\text{O-H=0.9724}\text{A}\text{?}\text{HOH=104.50°}\text{O-D=0.9687}\text{A}\text{?}\text{DOD=104.35°}\text{O-T=0.9671}\text{A}\text{?}\text{TOT=104.26°}$

A one-dimensional approximation to the anharmonicity effects is applied to determine the equilibrium molecular structure of H₂O from the average structure data. The result is as follows:

$\text{r}{}_{\mathrm{e}}\text{=0.9587}\text{A}\text{?}\text{and θ}{}_{\mathrm{e}}\text{=103.9°}$

     

Molecular beam electric resonance study of KCN,K13CN and KC15N

The microwave spectra of the isotopic species K¹³CN and KC¹⁵N have been investigated by molecular beam electric resonance spectroscopy, using the seeded beam technique. For both isotopic species about 20 rotational transitions originating in the ground vibrational state were observed in the frequency range 9–38 GHz. The observed transitions were fitted to an asymmetric rotor model to determine the three rotational, as well as the five quartic and three sextic centrifugal distortion constants. The hyperfine spectrum of KCN has been unravelled with the help of microwave-microwave double-resonance techniques. One hundred and forty hyperfine transitions in 11 rotational transitions have been assigned. The hyperfine structures of K¹³CN and KC¹⁵N were also studied. For all three isotopic species the quadrupole coupling constants and some spin-rotation coupling constants could be deduced. The rotational constants of the ¹³C and ¹⁵N isotopically substituted species of potassium cyanide, combined with those of the normal isotopic species (determined more accurately in this work), allowed an accurate and unambiguous evaluation of the structure, which was confirmed to be T shaped. Both the effective structure of the ground vibrational state and the substitution structure were evaluated. The results for the effective structural parameters are $\text{r}{}_{\mathrm{<mtext>CN</mtext>}}\text{= 1.169(3)}\text{A}\text{?}$, $\text{r}{}_{\mathrm{<mtext>KC</mtext>}}\text{= 2.716(9)}\text{A}\text{?}$, and $\text{r}{}_{\mathrm{<mtext>KN</mtext>}}\text{= 2.549(9)}\text{A}\text{?}$. The values obtained for the principal hyperfine coupling constant eQq_z(N), the angle between the CN axis and z_N, and the bond length r_CN indicate that in gaseous potassium cyanide the CN group can be considered as an almost unperturbed CN^? ion.     

The microwave spectrum and structure of chloromethyl cyclopropane

The microwave spectra of $\text{CH}{}_2\text{CH}{}_2\text{CH}$CH₂³⁵Cl and $\text{CH}{}_2\text{CH}{}_2\text{CH}$CH₂³⁷Cl have been observed and lines assigned to the gauche form. The rotational constants in MHz and distortion constants in KHz are: C₃H₅CH₂³⁵Cl, A = 11745.65, B = 2047.274, C = 1886.622, Δ_J = 0.85, Δ_JK = ? 0.9, Δ_K = 44., δ_J = ? 0.099, δ_K = 19.1, C₃H₅CH₂³⁷Cl, A = 11691.61B = 1997.664, C = 1842.823, Δ_J = 0.7, Δ_JK = ? 64.6, Δ_K = 2400, δ_J = 0.19, δ_K = ? 67.