Microwave spectrum,conformation, and quadrupole coupling constants of cyclopentyl chloride

The microwave spectra of the normal and two isotopic species of cyclopentyl chloride have been observed and analyzed. For the normal isotopic species the rotational constants (in MHz) are A = 4547.77 ± 0.01, B = 2290.22 ± 0.01, and C = 2073.34 ± 0.01. From the rotational constant data, it has been shown that the stable molecular conformation is the bent axial form. Quadrupole coupling constants have been measured for the ³⁵Cl nucleus, the values being (in MHz) χ_aa = ?23.70 ± 0.10, χ_bb = 32.33 ± 0.36, and χ_cc = ?8.63 ± 0.37. When transformed to the CCl bond axis system, the coupling constants confirm the axial structure. Extensive vibrational satellite structure, presumably arising from the pseudorotational ring mode with a fundamental frequency of 52 ± 5 cm^?1, has been observed and assigned. No spectral evidence has been observed for a second stable molecular conformer.     

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.     

Microwave spectrum,centrifugal distortion constants,and quadrupole coupling constants of 3-chloropyridine

The microwave spectrum of 3-chloropyridine has been measured in the frequency region of 8.2 to 18 GHz. The rotational constants, centrifugal distortion constants, and the quadrupole coupling constants for the ³⁵Cl species are A = 5839.448 ± 0.027 MHz, B = 1604.152 ± 0.005 MHz, C = 1258.327 ± 0.004 MHz, Δ_J = 0.10 ± 0.01 KHz, Δ_JK = 0.36 ± 0.09 KHz, Δ_K = 1.18 ± 0.07 KHz, δ_J = ?0.008 ± 0.005 KHz, δ_K = 0.88 ± 0.20 KHz, χ_aa = ?70.04 ± 0.38 MHz, χ_bb = 36.68 ± 0.19 MHz. The values of rotational constants and quadrupole coupling constants for the ³⁷Cl species are A = 5840.052 ± 0.034 MHz, B = 1559.354 ± 0.01 MHz, C = 1230.739 ± 0.016 MHz, χ_aa = ?54.20 ± 1.26 MHz, χ_bb = 29.49 ± 0.48 MHz. The double bond character in the CCl bond is found to be 2%. The smaller than expected value of rotational constant A points to a “fattening” of the pyridine ring about the a-axis in contrast to 2-chloropyridine, where no such substitution effect was observed.     

Microwave spectrum,structure, quadrupole coupling constants,dipole moment,and barrier to internal rotation of N-methylhydroxylamine

The microwave spectrum has been observed and analyzed for five isotopic species of N-methylhydroxylamine. For the normal species the rotational constants (in Megahertz) are A = 38 930.771 ± 0.005, B = 3939.607 ± 0.002, and C = 8690.716 ± 0.001. These data show that the molecule exists in the trans conformation, with structural parameters that include the following: CN = 1.460, NO = 1.461, NH = 1.007, and OH = 0.962. Hyperfine structure analyses have yielded the complete inertial axis ¹⁴N quadrupole coupling constant tensor, and thus the tensor values in the electric field-gradient principal axis system as follows: χ_xx = 4.41 ± 0.30, χ_yy = 1.93 ± 0.45, and χ_zz = ?6.34 ± 0.30 MHz. The total electric dipole moment has been found to have the value μ_T = 0.71 D, and the barrier to internal rotation of the methyl group is 3.55 kcal/mole.     

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,barrier to internal methyl rotation,dipole moment,and partial structure of dimethylketene

From the microwave spectrum of dimethylketene which has been recorded from 8 to 37 GHz, the following rotational constants were derived: A = 8 267.832 ± 0.8, B = 3 884.101 ± 0.03, C = 2 728.826 + 0.03 MHz. The dipole moment is μ_a = 1.94 ± 0.01 D. Substitution coordinates for all methyl group atoms have been obtained by investigating the spectra of six isotopic species of the molecule. The potential barrier V₃ hindering internal rotation of the methyl tops has been fitted to the multiplet width of a number of high-J ground state ^aQ-transitions which were observed as triplets. V₃ is 2065 cal/mole, keeping fixed I_α = 3.132 amu Ų and angle (methyl-top to a-axis) = 58.94° as obtained from the partial substitution studies.     

Microwave spectrum,quadrupole coupling constants,and barrier to internal rotation of 2-iodopropene

The microwave spectrum of 2-iodopropene has been investigated between 7.7 and 18 GHz. The measured transition frequencies of the ground and two vibrationally excited states have been analyzed using direct diagonalization of the rotational and quadrupole Hamiltonian. The following rotational and quadrupole coupling constants have been determined in a leastsquares fit for the ground state: A = 9285.153(20) MHz; B = 2337.2198(14) MHz; C = 1887.5871(14) MHz; and χ_cc = ?1820.783(33) MHz; χ_ab = 147.5(10) MHz; χ_bb = 957.018(41) MHz; and χ_cc = 863.765(40) MHz. The quadrupole coupling constants have been transformed to their principal axis system. From the splittings of some transitions of the first torsionally excited state a value of V₃ = 905(3) cm^?1 has been found for the threefold barrier hindering the internal rotation of the methyl group.     

The microwave spectrum of 4-pyridine carbaldehyde (isonicotinealdehyde)

The microwave spectrum of 4-pyridine carbaldehyde has been investigated in the region 8 to 40 GHz. Rotational transitions have been observed and assigned for the ground state and two excited states of the torsion mode. Analysis yields precise rotational constants (A = 5519.04 ± 0.08, B = 1559.17 ± 0.03, C = 1216.11 ± 0.02 MHz) which prove the molecule to be planar. Centrifugal distortion constants have also been obtained. Analysis of the observed ¹⁴N quadrupole fine structure yields the following quadrupole coupling constants (in MHz): χ_aa = ?4.67 ± 0.09; χ_bb = 1.19 ± 0.26; χ_cc = 3.48 ± 0.26. The electric field gradient about the nitrogen nucleus is thus similar to that of pyridine.     

Infrared,Raman, and microwave spectra of ethaneselenol and the determination of the barriers to internal rotation

The infrared, Raman, and microwave spectra of gaseous ethaneselenol have been investigated. The rotational constants for both the more stable gauche and for the trans conformers are reported for the Et⁷⁸SeH, Et⁷⁸SeD, Et⁸⁰SeH, and Et⁸⁰SeD isotopic species. A proposed structure has been derived from a least-squares analysis of the moments of inertia. Dipole moment components have been obtained from each conformer using second-order Stark effects. For the gauche conformer, they are μ_a = 1.42 ± 0.01, μ_c = 0.37 ± 0.03, and μ_total = 1.47 ± 0.01 D. For the trans isomer they are μ_a = 1.217 ± 0.002, μ_b = 0.850 ± 0.001, and μ_total = 1.485 ± 0.002 D. The methyl barrier to internal rotation was calculated using observed frequencies obtained from the infrared and Raman spectra; a value of 3.59 ± 0.01 kcal/mole was obtained. Asymmetric potential functions have been calculated for both the EtSeH and EtSeD isotopic species. For the light species the potential constants for internal rotation around the CSe bond are V₂ = ?96.4 ± 1, V₃ = 432 ± 4, and V₆ = ?20 ± 2 cm^?1. The difference between ground-state energy levels of the two conformers was found to be 66 cm^?1. A vibrational assignment based on infrared and Raman spectra of the gaseous phase is presented.     

Microwave spectrum,molecular structure,and nuclear quadrupole coupling constants of 3-bromopropene

The microwave spectra of the two ⁷⁹Br and ⁸¹Br isotopic species of 3-bromopropene were measured in the frequency region 14–23 GHz. The R and Q branches for a- and b-type rotational transitions of one conformer, skew, have been assigned and the rotational constants of the ground state have been determined to be A = 19 247.56 MHz, B = 1975.339 MHz, and C = 1914.761 MHz for ⁷⁹Br species, and A = 19 234.26 MHz, B = 1961.417 MHz, and C = 1901.563 MHz for ⁸¹Br species, respectively. By the analysis of the second-order perturbation treatment of the quadrupole interaction, it is found that the χ_ab element of the χ tensor primarily contributes to the anomalous hyperfine splittings. The matrix elements of products of direction cosines in terms of the symmetric top wavefunctions have been derived. The nuclear quadrupole coupling constants have been determined χ_aa = 384.2 MHz, χ_bb = ?71.9 MHz, χ_cc = ?276.3 MHz, and |χ_ab| = 358.7 MHz for ⁷⁹Br species and χ_aa = 283.2 MHz, χ_bb = ?55.6 MHz, χ_cc = ?227.6 MHz, and |χ_ab| = 296.0 MHz for ⁸¹Br species.     

Microwave spectrum of 3-cyanocyclopropene

Microwave measurements of the normal isotopic species of 3-cyanocyclopropene have given the following ground vibrational state rotational constants: A = 19876.036 ± 0.006, B = 3533.743 ± 0.001, and C = 3417.839 ± 0.001 MHz. The value of the ¹⁴N quadrupole coupling constant χ_cc was found to be 1.62 ± 0.05 MHz, and the molecular dipole moment had a value of μ_T = 4.47 ± 0.04 Debye. The results are compared to those for related molecules, and are discussed qualitatively with respect to the molecular structure.     

Rotation-inversion spectrum of methylaminoethane

Microwave spectral assignments have been made for the ground and several excited vibrational states of the normal and amino d₁ species of methylaminoethane. The inversion-rotation spectrum is consistent with a trans rotameric form with an amino inversion barrier of ～5.2 kcal mole^?1. The dipole moment of 8.88 ± 0.02 Debye has components |μ_a| = 0.00 ± 0.03, |μ_b| = 0.25 ± 0.03, and $\text{|〈 ± μ}{}_{\mathrm{c}}\text{? 〉| = 0.84 ± 0.01}$ Debye. The normal species N¹⁴ nuclear quadrupole coupling constants are (in MHz) 2.82 ± 0.09, 0.88 ± 0.13, and ?3.70 ± 0.09 for χ_aa, χ_bb, and χ_cc, respectively.     

Microwave spectrum of nitroxyl

The microwave spectrum of HNO has been observed and analyzed. Both a-type and b-type transitions have been measured. The rotational constants obtained are A = 553903.0 ± 2.7 MHz, B = 42308.52 ± 0.10 MHz, and C = 39169.46 ± 0.10 MHz. In the analysis of the spectrum, centrifugal distortion corrections are tentatively taken into account by using the centrifugal distortion constants determined by Dalby. The quadrupole coupling constants for nitrogen in HNO are determined to be χ_aa = 0.36 ± 0.56 MHz, χ_bb = ? 5.46 ± 0.30 MHz, and χ_cc = 5.10 ± 0.26 MHz. The dipole moment and its components determined from the Stark effect measurement are μ_total = 1.67 ± 0.03 D, μ_a = 1.03 ± 0.01 D, and μ_b = 1.31 ± 0.02 D. The microwave spectrum of DNO has been reanalyzed by taking into account the centrifugal distortion effect. The inertia defects for HNO and DNO have been calculated. The results are limited in precision by the lack of reliable force constants.     

Electronic structure of arsabenzene: Microwave spectrum,dipole moment,and nuclear quadrupole coupling constants

The microwave spectrum of arsabenzene was analyzed; a dipole transitions were observed. The following rotational constants were obtained; A = 4871.03 ± 0.18 MHz, B = 2295.87 ± 0.01 MHz, C = 1560.10 ± 0.01 MHz. The dipole moment was 1.10 ± 0.04 D. The nuclear quadrupole coupling constants due to the ⁷⁵As nucleus were χ_aa = ?186.4 ± 0.1 MHz, χ_bb = 43.5 ± 0.2 MHz, χ_cc = 142.9 ± 0.2 MHz, and the asymmetry parameter, η = 0.533 ± 0.002. Analysis of the quadrupole coupling constants indicated that the population of the 4p orbitals on arsenic decrease in the order n_a > n_b > n_c.     

Microwave spectrum and substitution structure of methylene chloride

The microwave spectrum of methylene chloride has been reinvestigated in order to obtain a complete substitution (r_s) structure of well-defined precision. Measurements on the ¹³CH₂Cl₂ species have yielded the following rigid-rotor rotational constants: A = 30746.20 ± 0.10 MHz, B = 3320.63 ± 0.11 MHz, and C = 3053.44 ± 0.10 MHz. These data, combined with revised values reported earlier for other isotopic species, yields the following r_s structural parameters: CCl = 1.767 ± 0.002 Å, CH = 1.085 ± 0.002 Å, ∠HCH = 112.1 ± 0.2°, and ∠ClCCl = 112.2 ± 0.1°.     

Microwave spectrum,quadrupole coupling constant,and conformation of 1-cyanocyclohexene

The microwave spectrum of 1-cyanocyclohexene has been investigated in the frequency regions 8–12.4 and 18–26.5 GHz. A-Type transitions in the ground state and three excited states have been assigned. The rotational constants in the ground state were determined to be A = 4565.98 ± 0.46, B = 1423.44 ± 0.01, and C = 1136.17 ± 0.01 MHz. From the experimental data, it was suggested that the molecule has an equilibrium half-chair conformation similar to those of cyclohexene and 1-fluorocyclohexene. From the hyperfine splittings of the ¹⁴N nucleus, the quadrupole coupling constant, X_aa, was found to be 4.2 MHz.     

Microwave spectrum of 2-chloropyridine

The microwave spectrum of 2-chloropyridine, C₅H₄NCl, has been studied in the frequency range from 26.5–40.0 GHz. The spectrum is characterized by strong parallel type transitions of a near-prolate asymmetric top. The assigned transitions have been used to evaluate the ground state rotational constants of the two chlorine isotopes. The rotational constants are (in MHz): A = 5872.52, B = 1637.83, C = 1280.48 for the ³⁵Cl isotopic species and A = 5872.16, B = 1591.76, C = 1252.17 for the ³⁷Cl isotopic species. The small inertial defect indicates the molecule is planar. In addition an excited vibrational state of C₅H₄N³⁵Cl has been observed and analyzed. The chlorine quadrupolar coupling constants were determined for the ground state and are: χ_aa = ?71.9 MHz for ³⁵Cl and χ_aa = ?54.9 MHz for ³⁷Cl. By assuming the pyridine ring structure the CCl bond length is found to be 1.72 Å.     

The microwave spectrum of trans-ethylamine

The microwave spectrum of normal trans-ethylamine CH₃CH₂NH₂ and that of the -NHD and -ND₂ species were measured and assigned. The obtained rotational constants for the ground state of the normal species are (in MHz): A = 31 758.33 ± 0.08, B = 8749.157 ± 0.025, and C = 7798.905 ± 0.025. The fitted dipole moment components are (in Debye): |μ|_a = 1.057 ± 0.006, |μ_b| = 0.764 ± 0.009, and |μ_t| = 1.304 ± 0.011. The quadrupole coupling constants were fitted as (in MHz): χ⁺ = 1.62 ± 0.035 and χ^? = ?1.89 ± 0.08. Analysis of the HFS of the deuterated species -ND₂ allowed the experimental determination of the principal quadrupole tensor values (in MHz): χ_zz = ?4.68 ± 0.20, χ_yy = 1.75 ± 0.06, and χ_xx = 2.93 ± 0.20. The angle between the CN bond and the direction of the χ_zz quadrupole tensor component was fitted as 108.9° ± 0.6° and agreed with the expected general direction of the lone electron pair.     

Internal rotation and inversion doubling in the microwave spectrum of CH3NHCl

The microwave “a” and “c” type spectra of four isotopic species of CH₃NHCl in the ground state and of CH₃NHCl³⁵ and CH₃NDCl³⁵ in the first excited torsional state have been analyzed. From the A-E torsional splittings of the excited state the torsional barrier height has been determined to be V₃ = 3710 ± 46 cal/mole. The “c” type transitions show an inversion doubling of 4.60 ± 0.10 MHz in the ground state and of 5.25 ± 0.10 MHz in the first excited torsional state. Such doublings are independent on the rotational quantum numbers within the experimental errors. The height of the inversion barrier has been roughly evaluated by using the Dennison-Uhlenbeck potential.     

Microwave spectrum,conformation, and dipole moment of 4-thiacyclohexanone

The microwave spectra of 4-thiacyclohexanone in the ground state and eight vibrationally excited states have been studied in the frequency region 18.0–40.0 GHz and the corresponding rotational constants have been determined. The following values of the ground-state rotational constants (MHz) were obtained from the analysis of the a-type transitions: A = 3935.149 (0.031), B = 1829.444 (0.001), and C = 1364.609 (0.001). Analysis of the Stark effect gives for the dipole components (in Debye units) μ_a = 1.409 (0.002), μ_c = 0.391 (0.064). These data are consistent with a chair conformation for the ring. A phisically reasonable set of structural parameters which reproduce the ground-state rotational constants has been derived. A qualitative estimate of the low-frequency vibrational modes was obtained from relative-intensity measurements. The lowest vibrational frequency is believed to be a ring-bending mode and it occurs at 77 ± 22 cm^?1 while the ring-twisting mode is at 204 ± 27 cm^?1.