Microwave spectrum, structure, dipole moment, and internal rotation of fluoromethyl methyl ether

Microwave spectra of fluoromethyl methyl ether and its 10 isotopically substituted species were measured. The r_s structure of this molecule was determined from the observed moments of inertia. Structural parameters obtained for this molecule, which was in the gauche form, were compared with those of the analogous molecules. Dipole moments of the normal and two deuterated species were determined by Stark-effect measurements. For the normal species, the dipole moment is 1.744 ± 0.029 D making an angle of 100°54′ with the O---CH₂ bond toward the C---F direction and lies in the plane whose dihedral angles with the FCO and COC planes are 114°9′ and 44°56′, respectively. The barrier to internal rotation of the methyl group was calculated taking into account the coupling effect with the skeletal torsion using the observed splitting data of the spectra in the ground, first excited methyl torsional, and skeletal torsional states. The barrier, skeletal torsional frequency, and coupling term were determined to be V₃ = 1538 ± 40 cal/mole, ω_t = 158 ± 4 cm⁻¹, and V_s = 490 ± 500 cal/mole, respectively.     

The microwave spectrum of 1-phosphabut-3-ene-1-yne, CH2=CHCP

The new molecule 1-phosphabut-3-ene-1-yne, CH₂=CHCP, produced by pyrolyzing prop-1-ene-3-phosphorus dichloride, CH₂=CHCH₂PCl₂, was detected by microwave spectroscopy. The analysis of the rotational transitions indicates that the molecule is planar with constants: A₀ = 46 694(24), B₀ = 2807.7100(21), and C₀ = 2645.8356(21) MHz. These rotational constants indicate that the structure of the vinyl group is essentially the same as that in CH₂=CHCN and CH₂=CHCCH; r(C---C) = 1.432 Å and (C=C---C) = 123.9°. The dipole moment parameters are μ_A = 1.181(2), μ_B = 0.074(1), and μ = 1.183(2) D. The vibrational satellite spectra for the C---CP bending modes indicate that ν₁₁(a′) = 184 ± 30 cm⁻¹ and ν₁₅(a″) = 263 ± 30 cm⁻¹.     

The microwave spectrum of phosphabutadiyne, H---CC---CP

A detailed rotational analysis of the microwave spectrum between 26.5 and 40 GHz of phosphaethene, CH₂=PH, has been carried out. This molecule is the simplest member of a new class of unstable molecules—the phosphaalkenes. The species can be produced by pyrolysis of (CH₃)₂PH, CH₃PH₂ and also somewhat more efficiently from Si(CH₃)₃CH₂PH₂. Full first-order centrifugal distortion analyses have been carried out for both ¹²CH₂³¹PH and ¹²CH₂³¹PD yielding: A₀ = 138 503.20(21), B₀ = 16 418.105(26), and C₀ = 14 649.084(28) MHz for ¹²CH₂³¹PH. The 1₀₁-0₀₀ μ_A lines have also been detected for ¹³CH₂PH, cis-CDHPH and trans-CHDPH. These data have enabled an accurate structure determination to be carried out which indicates: r(H_cC) = 1.09 ± 0.015 Å, (H_cCP) = 124.4 ± 0.8°; r(H_tC) = 1.09 ± 0.015 Å, (H_tCP) = 118.4 ± 1.2°; r(CP) = 1.673 ± 0.002 Å, (HCH) = 117.2 ± 1.2°; r(PH) = 1.420 ± 0.006 Å, (CPH) = 97.4 ± 0.4°. The dipole moment components have been determined as μ_A = 0.731 (2), μ_B = 0.470 (3), μ = 0.869 (3) D for CH₂PH; μ_A = 0.710 (2), μ_B = 0.509 (10), μ = 0.874 (7) D for CH₂PD.     

The microwave spectrum, structure, chlorine nuclear quadrupole coupling constants, dipole moment, and centrifugal distortion constants of dichlorosilane

The microwave spectra of three isotopic species of dichlorosilane, SiH₂Cl₂, in its ground vibrational state, have been measured in the frequency region 8–40 GHz. The spectra have yielded values for the rotational constants, centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 1.13 ± 0.02 D. The molecule has C_2v symmetry, and the bond lengths and angles r(Si---Cl=2.033±Å, r(Si---H)=1.480±0.015Å, (Cl---Si---Cl)=109°43′±20±, (H---Si---H)=111°18′±40′ The centrifugal distortion constants have been compared with those calculated using a published force field.     

Rotational Spectra of CH2DCCH and CH3CCD: Experimental and ab Initio Equilibrium Structures of Propyne

The ground state rotational spectra of CH₂DCCH and CH₃CCD (main species and ¹³C-substituted species) have been measured up to 470 GHz. Accurate rotational and centrifugal distortion constants have been determined. r₀, r_s, r_ε,I, and r^ρ_m, structures of propyne have been calculated. The ab initio structure has also been calculated using three different methods (SCF, MP2, and QCISD) and two basis sets (DZP and TZ2P). Offsets have been derived empirically using molecules containing structural units present in propyne and whose equilibrium structures have been determined previously. A near-equilibrium structure has been estimated to be acetylenic r(C---H) = 1.061 (1) Å, r(CC) = 1.204 (1) Å, r(C---C) = l.458 (2) Å, methyl r(C---H) = 1.089 (1) Å, and (CCH) = 110.7 (5)°.     

Microwave spectrum, molecular structure, dipole moment, and theoretical calculation of cyclopentanone oxime

The microwave spectra of cyclopentanone oxime (C₅H₈NOH) and its deuterated species (C₅H₈NOD) were observed in the frequency region from 9 to 40 GHz. Only a-type R-branch transitions were assigned in the vibrational ground and excited states. The rotational constants of normal species were determined to be A = 5870.80(33), B = 1917.021(8), and C = 1526.784(8) MHz in the vibrational ground state, and A = 5870.16(43), B = 1842.707(9), and C = 1479.401(9) MHz for deuterated species. The dipole moments were determined as μ_a = 0.80(10), μ_b = 0.20(10), and μ_c = 0.40(10) D. The ring-puckering vibrational states were observed up to v = 6. The vibrational mode was nearly harmonic. The fundamental frequency of the ring-puckering mode was found to be 70(20) cm⁻¹. The molecular structure of cyclopentanone oxime was determined to be a twisted configuration by comparing the observed and calculated rotational constants, planar moment of inertia, P_cc, and r_s coordinates of the hydroxyl hydrogen atom. On the molecular geometry, the bond angle, C₂C₁N₆ (Fig. 1), is larger than C₅C₁N₆ by ca. 6°, because of the steric repulsion between the methylene group of C₂ atom and hydroxyl group.     

Microwave spectrum,structure, dipole moment,and internal rotation of the trans isomer of ethyl methyl sulfide

The microwave spectra of the trans isomer of ethyl methyl sulfide and its 10 isotopic species were measured. The r_s structure of this isomer was determined from the observed moments of inertia. The dipole moment and its direction in the molecule were determined by Stark effect measurements of low J transitions for the normal and CH₃CH₂SCD₃ species. The barrier to internal rotation of the SCH₃ group was calculated from the observed A-E splittings of the transitions. The present results were compared with those for the analogous molecules.     

Molecular structure, nuclear quadrupole coupling constant and dipole moment of nitrogen trichloride from microwave spectroscopy

The rotational constants of four isotopic species of nitrogen trichloride have been obtained from transitions in the millimeter region. Two r_s structures have been obtained with the following average values of the parameters. rN−C1=1.7535 ± 0.0020 A.The Stark effect of the J = 3 ← 2 transition was analyzed to obtaine the value 0.39 ± 0.01 D for the dipole moment of NCl₃. The measurement of the separation of the two strongest hyperfine components of the J = 2 ← 1 transition yielded the value of −108 ± 3 MHz for the N---Cl bond axis quadrupole coupling constant.     

Determination of the Splitting of the 6a0 and 6b0 Bands of C-Hexadeuterobenzene in a Supersonic Jet

By using resonance-enhanced two-photon ionization, rotationally resolved spectra of the 6¹₀ band of ¹²C₆D₆ and (¹³C¹²C₅D₆ molecules have been obtained for the first time at a rotational temperature of 0.7 K in a pulsed supersonic beam. From the former, the values of B″ = 0.1573 ± 0.0008 cm⁻¹, B′ = 0.1508 ± 0.0008 cm⁻¹, and ξ′ = −0.412 ± 0.050 have been derived for rotational and Coriolis constants in the lower and upper levels of ¹²C₆D₆. Also, the spectra corresponding to ¹²C₆H₆ and ¹³C¹²C₅H₆ have been measured and the values B″ = 0.1892 ± 0.0008 cm⁻¹, B′ = 0.1815 ± 0.0008 cm⁻¹, and ξ′ = −0.586 ± 0.050 have been obtained for ¹²C₆H₆, in agreement with previous results. Rotational constants of ¹³C labeled benzene molecules have been geometrically deduced from the constants obtained. Experimental isotopic shifts of the vibronic origins of the 6a¹₀ and 6b¹₀ bands have been determined. There is agreement with previous ¹³C-benzene-h₆ data. The present results are −0.91 ± 0.05 and 3.09 ± 0.05 cm⁻¹ for ¹³C¹²C₅D₆ and −1.64 ± 0.05 and 2.64 ± 0.05 cm⁻¹ for ¹³C¹²C₅H₆. The splittings of vibrational modes 6b and 6a in the ¹B_2u state are 4.00 ± 0.10 cm⁻¹ for ¹³C¹²C₅D₆ and 4.28 ± 0.10 cm⁻¹ for ¹³C¹²C₅H₆.     

Doppler-limited dye laser excitation spectroscopy of DCF

The dye laser excitation spectrum of the vibronic transition of DCF was observed between 17 200 and 17 400 cm⁻¹ with the Doppler-limited resolution. DCF was produced by the reaction of microwave-discharged CF₄ with CD₃F. The observed spectra, which were found to be nearly free of perturbations, were assigned to 858 transitions of the K′_a − K″_a = 4−5, 3−4, 2−3, 1−2, 0−1, 1−0, 2−1, 3−2, 3−3, 2−2, 1−1, 0−0, 2−0, and 0−2 subbands, and were analyzed to determine the rotational constants and centrifugal distortion constants for both the and à states. The rotational constants of DCF thus determined were combined with those of HCF to calculate the structural parameters for this molecule: r(C---H) = 1.138 Å, r(C---F) = 1.305 Å, and HCF = 104.1° for the ground state, and r(C---H) = 1.063 Å, r(C---F) = 1.308 Å, and HCF = 123.8° for the excited à state.     

Barriers to internal rotation in asymmetric molecules: 2,3-Difluoropropene

The potential function for internal rotation in 2,3-difluoropropene has been obtained from the microwave spectrum of the gauche rotamer, the far- and mid-infrared spectra of both the gauche and cis rotamers and the absolute rotational intensity measurements of several gauche microwave transitions. It is found that the cis conformer is most stable by 145 ± 60 cm⁻¹. Both the cis-gauche and gauche(+)-trans-gauche(−) barriers are approximately 1000 cm⁻¹. A comparison between the potentials in 2,3-difluoropropene, propene, and several other fluoropropenes is made. The dipole moment of the gauche conformer is μ_a = 0.950 D, μ_b = 1.982 D, and μ_c = 1.135 D; μ_total = 2.67 D.     

Line Intensities in the ν1, ν3, and 2ν2 Bands of H2Se

Using a high-resolution Fourier transform spectrum of hydrogen selenide in natural abundance, about 600 intensities of lines belonging to the ν₁, ν₃, and 2ν₂ bands of H₂⁸⁰Se were measured. A least-squares fit of these intensities was performed, allowing determination of the vibrational transition moments of these bands and their rotational corrections. Finally, the first derivatives of the dipole moment with respect to the normal coordinates q₁ and q₃ were found to be ∂μ_χ/∂q₁ = (−0.5938 ± 0.010) × 10⁻¹ and ∂μ_z/∂q₃ = (0.5683 ± 0.010) × 10⁻¹ Debye, respectively.     

predictions of PMNS and CKM angles

Generalizing a previous model to accommodate the third quark family and CP violation, we present a T^′ model which predicts tribimaximal neutrino (PMNS) mixings while the central predictions for quark mixings are |V_td/V_ts|=0.245 and |V_ub/V_cb|=0.237 with a predicted CP violating KM phase δ_KM=65.8°. All these are acceptably close to experiment, including the KM phase for which the allowed values are 63°<δ_KM<72°, and depend only on use of symmetry T^′×Z₂ to define the model and no additional parameters.     

Millimeter-Wave Spectroscopy, High-Resolution Infrared Spectrum, ab Initio Calculations, and Molecular Geometry of FPS

The transient thiophosphenous fluoride FPS was produced by pyrolysis of 2.5% F₂PSPF₂ in Ar at 1300–1800°C. High-resolution (≥0.004 cm⁻¹) Fourier transform infrared spectra of the a-type ν₁ and b-type ν₂ bands, centered respectively at 803.249 and 726.268 cm⁻¹, were measured and fitted to rotational and quartic centrifugal distortion parameters. The millimeter-wave spectrum, essentially b-type, was measured between 300 and 370 GHz in the ground state and in the ν₃ excited state for FP³²S and in the ground state for FP³⁴S. The frequencies were fitted to a Watson-type A-reduced Hamiltonian up to sextic distortion terms. High level ab initio calculations with large basis sets were performed on FPS and supported the first identification of its infrared and millimeter wave spectra. The calculated anharmonic force field provided precise ab initio rovibrational α constants which were combined with the experimental molecular parameters to determine an accurate equilibrium structure of the molecule: r_e(PS)=188.86 pm, r_e(PF)=158.70 pm, θ(FPS)=109.28°. The collision-controlled 1/e lifetime measured in a 10-Pa (1 : 20) F₂PSPF₂/Ar mixture was 2 s, more than two orders of magnitude larger than that of FPO under the same experimental conditions.     

Infrared and microwave spectra, molecular conformation and electric dipole moment of methyl thiolformate

The microwave spectrum (41-10 GHz) and the infrared spectrum (4000-50 cm⁻¹) of methyl thiolformate have been obtained and analyzed. The spectra are consistent with a single molecular conformation having a planar array of heavy atoms and with the alkyl group cis to the carbonyl group. The measured rotational constants are: A, 11042.22 MHz; B, 5118.27 MHz; C, 3562.03 MHz (κ = −0.5839). No internal rotation doublets were observed in the microwave spectrum for the ground vibrational state, which implies that the barrier hindering internal rotation of the methyl group is either much larger or much smaller than the corresponding value for methyl formate. If the former is true then a lower limit of 10.5 kJ mol⁻¹ may be placed on the barrier height.The dipole moment of methyl thiolformate was measured using the Stark effect to be 1.58 ± 0.05 Debyes (μ_A = 1.52 D; μ_B = 0.43 D) for the vapor, and for dilute solutions in benzene at 295 K the value of 1.6 ± 0.1 D was found from capacitance measurements.SCF computations using minimal basis sets of STO/3G atomic orbitals and extended basis sets of STO/4.31G atomic orbitals have been carried out for methyl thiolformate and methyl formate. Energy differences between rotational isomers and estimates of barrier heights are given together with the calculated dipole moments.     

The harmonic force field and ground-state average structure of difluoroborane

An improved harmonic force field of difluoroborane has been calculated using the vibrational wavenumbers and quartic centrifugal distortion constants of four isotopic species. The unidentified vibrational mode ν₅ is predicted at 1049 ± 50 and 775 ± 50 cm⁻¹ for HBF₂ and DBF₂, respectively. The ground-state average structure of HBF₂ has been found to be r_z(BH) = 1.195 ± 0.003 Å; r_z(BF) = 1.315 ± 0.001 Å; (FBF) = 118.0 ± 0.1°.     

Isoscalar quadrupole strength in Ca from the (p,p′α0) reaction at Ep = 100 MeV

The ⁴⁰Ca(p,p′ α) reaction has been studied at an incident proton energy E_p = 99.5 MeV for proton laboratory scattering angles Θ_p^lab = 17°, 23° and 27°. Emission of α particles coincident with the scattered proton has been measured for an angular range Θ_α 0° − 180° relative to the recoil axis. A multipole decomposition for the α₀-decay channel to the ³⁶Ar ground state has been performed from the angular-correlation functions. The energy distribution of the dominating E2 strength deduced in the excitation energy range E_x = 11–21 MeV agrees reasonably well with the results from electron and α-induced α₀-decay investigations. The exhaustion of the E2 energy-weighted sum rule in this channel up to an energy of 17 MeV is 16.1(4.0)%, in accord with the study of the (α, α′ α₀) reaction. However, this value is twice what is found in the (e,e′ α₀) experiment in the same energy region. Thus, the puzzling discrepancy in the E2 strengths derived from electromagnetic and hadronic probes remains unsolved.     

Microwave spectrum and structure of ethylene ozonide: Effects of large axes rotations in structure calculations

Rotational spectra for 14 isotopic species of ethylene ozonide have now been assigned. The consistency of the Kraitchman substitution structure was checked by calculating the O_p---O_p bond distance six ways; the values ranged from 1.458 to 1.502 Å. This variation was attributed to an amplification of residual vibrational effects by large axes rotations upon isotopic substitution. Estimates of errors produced from this effect were made and a procedure was developed for choosing r_s parameters in which the effect is minimized. This gave the following ring parameters: d(CO_e) = 1.416 Å, d(CO_p) = 1.412 Å, d(OO) = 1.461 Å, <CO_eC = 104.8°, <O_eCO_p = 105.5°, <CO_pO_p = 99.3°.     

The methyl bromide molecule: A critical consideration of perturbations in spectra

This work gives an extensive critique of studies on methyl bromide and all its isotopic varieties with special stress on their rotational, vibrational, and rovibrational spectra. The rotational constants of more than 40 vibrational states of CH₃Br and 20 of CD₃Br, as well as of the ground states of all varieties, were critically examined and corrected where needed. An almost complete set of harmonic and anharmonic constants for CH₃Br was derived. From the set of rotation-vibration interaction constants, new accurate equilibrium constants A_e and B_e have been evaluated for CH₃⁷⁹Br, CH₃⁸¹Br, CD₃⁷⁹Br, CD₃⁸¹Br, from which the following equilibrium structure is obtained: r_e(C---H) = 1.0823 Å; r_e(C---Br) = 1.9340 Å; α(HCH) = 111.157°.     

Microwave spectrum and conformation of 6-thiabicyclo[3.1.0]hexane

The microwave spectrum of 6-thiabicyclo[3.1.0]hexane (cyclopentene sulfide) has been measured in the region 26,500-40,000 MHz. The experimental data are consistent with a single stable conformation. Furthermore, these data can only be satisfactorily explained by assuming that this conformation is the boat form. Rotational constants were obtained, both for the ground state and two excited vibrational states, while centrifugal distortion coefficients were obtained for the ground state and one excited vibrational state. The ground state rotational constants found were A₀ = 5026.243 ± 0.003 MHz, B₀ = 2833.813 ± 0.003 MHz, and C₀ = 2411.679 ± 0.03 MHz. For the ground state of the molecule, the electric dipole moment components were found to be μ_a = 1.800 ± 0.012 D and μ_c = 1.155 ± 0.024 D, yielding a total dipole moment μ = 2.139 ± 0.027 D.