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1.
The rotational spectrum of the unstable molecule selenoacetaldehyde, CH3CHSe, has been studied by microwave spectroscopy between 26.5 and 40 GHz. Transitions have been measured for five abundant selenium isotopic variants. These measurements have, together with structural information from the related molecules CH3CHS and CH3CHO, allowed reliable data on the C=Se bond length (1.758 ± 0.01 Å) and the
e angle (125.7 ± 0.3°) to be derived. The spectral lines show splittings due to hindered internal rotation and using these together with the derived structure, barrier heights of 1602 cal mole−1 (6703 J mole−1) and 1648 cal mole−1 (6859 J mole−1) have been determined for the ground and first torsionally excited states, respectively. 相似文献
2.
Measurements of rotational transitions of 1-butyne have been made in the range of ~20–130 GHz. Both a-type transitions up to J = 46 and b-type transitions up to J = 42 have been measured and fitted to a rotational Hamiltonian which includes centrifugal distortion terms. In addition to the five quartic centrifugal distortion constants, three sextic coefficients had to be included to reproduce the observed frequencies to within experimental error. The results of the analysis are sufficient for the prediction of all strong transitions throughout the millimeterwave range. A barrier to internal rotation of the methyl group of 3.260 kcal/mole (1 kcal/mole = 4.18 kJ/mole) has been derived from the first excited torsional state. Analysis of the second-order Stark effect has led to an accurate determination of both μa and μb with μa = 0.763(3) D and μb = 0.170(4) D. 相似文献
3.
The rotational spectra of the v6 = 1 and v6 = 2 torsional states of CH3C35Cl3 have been measured in the millimeterwave range and accurate spectroscopic constants have been determined. The equilibrium structure, the torsional frequency and the barrier to internal rotation have been calculated ab initio. These results are shown to be compatible with the absence of splittings in the rotational spectra. 相似文献
4.
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 Ic-Ia-Ib value of 0.1333 amu , spectral assignments of seven other isotopic modifications have resulted in the following substitution bond lengths and angles: CHsyn = 1.085 Å, CHanti = 1.077 Å, CS = 1.610 Å, SO = 1.469 Å, ?HCH = 121.86°, ?SCHsyn = 122.51°, ?SCHanti = 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 SO 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. 相似文献
5.
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 μa = 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 Iα = 3.132 amu Å2 and angle (methyl-top to a-axis) = 58.94° as obtained from the partial substitution studies. 相似文献
6.
Microwave spectra of methylpropargylether and its nine isotopically substituted species were measured. The plausible structure of this molecule was determined from the observed moments of inertia. The rs structural parameters of the OCH3 part of the molecule could be obtained and were compared with the corresponding parameters of the analogous molecules. The dipole moment and its direction in the molecule were determined by Stark-effect measurements. The barrier to internal rotation of the methyl group was determined from the A-E splittings of the spectra reported by K. M. Marstokk and H. Møllendal (J. Mol. Struct. 32, 191–202 (1976) taking into account the coupling effect of the skeletal torsion. 相似文献
7.
《Journal of Molecular Spectroscopy》1987,122(1):1-8
Microwave spectra of methylsilylsulfide and its three isotopically substituted species were measured and their b-type transitions were assigned. The spectra of all the species exhibit doublet structures due to the internal rotation of the methyl group. Using the internal axis method, the potential barriers were determined from the observed A- and E-component frequencies to be 1081.0 ± 3.3, 1073.9 ± 2.0, 1065.1 ± 11.4, and 1076.0 ± 1.9 cal/mol for the normal, CH3SSiD3, CD3SSiH3, and 13CH3SSiH3 species, respectively. The analysis also yielded 3°49′ as the tilt angle of the methyl top. From the rotational constants obtained, a plausible structure was estimated. The molecular electric dipole moments were determined from the second-order Stark effect of some A-component transitions with low- J quantum numbers for the normal and SiD3 species. A comparison of the obtained parameters was made with analogous molecules. 相似文献
8.
A detailed rotational analysis of the microwave spectrum between 26.5 and 40 GHz of phosphaethene, CH2PH, 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 101-000μA 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: . The dipole moment components have been determined as μA = 0.731 (2), μB = 0.470 (3), μ = 0.869 (3) D for CH2PH; μA = 0.710 (2), μB = 0.509 (10), μ = 0.874 (7) D for CH2PD. 相似文献
9.
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: χxx = 4.41 ± 0.30, χyy = 1.93 ± 0.45, and χzz = ?6.34 ± 0.30 MHz. The total electric dipole moment has been found to have the value μT = 0.71 D, and the barrier to internal rotation of the methyl group is 3.55 kcal/mole. 相似文献
10.
The microwave spectrum of the unstable thiocarbonyl thioketen, H2CCS, 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: , , , ∠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. 相似文献
11.
Microwave spectra of fluoromethyl methyl ether and its 10 isotopically substituted species were measured. The rs 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, ωt = 158 ± 4 cm−1, and Vs = 490 ± 500 cal/mole, respectively. 相似文献
12.
Microwave spectra of the ground and first three excited torsional states of N-sulphinylaniline have been assigned. The variation of the inertial defect with torsional number shows the molecule to be planar. The torsional frequency has been determined as ν = 41.1 cm?1 and the barrier to internal rotation as V2 = 2.3 kcal/mole. From the splittings of the Stark lobes of some lines the values μa = 2.20 ± 0.06, μb = 0.664 ± 0.005, and μtot = 2.30 ± 0.06 were obtained. 相似文献
13.
14.
Herbert M. Pickett 《Journal of Molecular Spectroscopy》1973,46(3):335-340
The microwave spectra of three isotopic species of amino acetonitrile (NH2CH2CN, NHDCH2CN, and ND2CH2CN) have been investigated to learn something about the structure and bonding in this and similar compounds. The only rotamer observed is the form in which both NH bonds are gauche to the CN group and the structure is quite rigid. From the available data only the bond angles are well determined. The amino NCC angle is 114.5(3)°, the HCH angle is 103(2)°, the HNC angle is 109.6(4)°, and the HNH angle is 107(1)°. The dipole moment components are μa = 2.577(7) D and μb = 0.5754(10) D; these agree quite well in magnitude and direction with the sum of the acetonitrile and methyl amine dipoles. The rigidity of the molecule and its preference for the form in which the amino protons are closest to the triple bond confirms a suggestion based on earlier studies on similar molecules that there is a strong hydrogen bonding interaction between the amino group and the nitrile group, although in this molecule dipole-dipole forces also probably play a significant role in determining the structure and its rigidity. 相似文献
15.
The far-infrared spectra of the Q branches of hindered rotation in CH3OD and CD3OD have been investigated in the 80- to 250-cm?1 spectral region. The theoretical spectra are calculated using the full set of Kirtman constants and are compared with the experimental spectra of resolutions up to 0.13 cm?1. 相似文献
16.
The microwave spectrum of propiolyl fluoride has been observed in the frequency region 12.5–40 GHz. Rotational transitions have been assigned for the ground and two excited vibrational states of the normal isotopic species and for the ground vibrational state of the deuterated species. In each case, values for the rotational constants and centrifugal distortion constants have been obtained. The molecule has been shown to be planar and structural calculations suggest no anomalies in any of the internuclear parameters. Stark effect measurements have yielded a value of 2.98 ± 0.02 Debyes for the dipole moment. 相似文献
17.
Microwave spectra of methyl fluorosilane and its 20 isotopic species were measured. In order to determine the most reliable rs structure, atom coordinate values were obtained by solving the Kraitchman equations from several sets of the substituted and parent species and by averaging the solutions. For unreliable Kraitchman coordinate values, several trials were made in order to fix the values. The second difference method was also applied to the unreliable Kraitchman values. The dipole moment and its direction in the molecule were obtained by Stark-effect measurements for the normal and two deuterated species. From the A-E splittings of the observed spectra in the ground state for nine species, the barrier to internal rotation and the direction of the top axis of the methyl group were determined. It is noted that the top axes obtained from the structure and from the analysis of the A-E splittings do not coincide with each other. From the structural analysis the methyl group is found to tilt toward two hydrogen atoms on the silicon atom by about 1°45′, whereas the analysis of the A-E splittings shows the methyl group tilting toward the fluorine atom by about 37′. Comparison of the results was made among methyl fluorosilane, ethyl fluorosilane, ethyl fluoride, and methyl fluorogermane. 相似文献
18.
Microwave spectra of fluoromethylethylether and its 13 isotopically substituted species have been measured. The rs structure of the GT isomer of this molecule was determined from the observed moments of inertia. The structural parameters obtained are roughly close to those of fluoromethylmethylether and the GT isomer of chloromethylethylether. The dipole moments and their directions in the molecule were determined from the Stark effect measurements of several low-J transitions for the normal and two deuterated species. The dipole moment of the normal species was found to be 1.806 ± 0.012 D, making angles of 136°50′ and 107°40′ with the CF and FCH2O bonds, respectively. From the A-E splittings of the spectra in the first excited methyl torsional state, the barrier to internal rotation of the methyl group was calculated to be 3150 ± 50 cal/mole in the one-top approximation. 相似文献
19.
Charles W. Gillies 《Journal of Molecular Spectroscopy》1976,59(3):482-492
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 , , 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. 相似文献
20.
Measurements of the microwave spectrum of CF2 have been extended to include transitions up to J = 40. Using these extended measurements, a centrifugal distortion analysis has been performed and from the distortion constants, the force field, infrared spectrum, average structure, Coriolis coupling constants, and inertial defect have been calculated. The original assignment of the infrared spectrum has been confirmed. An improved value for the dipole moment, 0.469 ± 0.026 D, has been obtained. 相似文献