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1.
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 (μA = 1.52 D; μB = 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.  相似文献   

2.
The microwave spectrum of methyl thiolfluoroformate (FCOSCH3) is reported for the ground state and seven vibrational satellites. The methyl group is in the syn conformation to the carbonyl group. The dipole moment components are μa = 2.89(2) D, μb = 0.30(8) D, and μc = 0. Spacings of A and E levels due to methyl internal rotation are analyzed for the ground state, the first excited methyl torsional state, and the first excited skeletal torsional state. An anomalous sequence of A and E levels occurring in the latter satellite arises from torsional interaction, according to two-dimensional model calculations. Potential parameters consistent with the three observed level separations are V3 = 304(5) cm−1, V6 = 23(1) cm−1 for the methyl torsion and either k = 1.912 or k = 2.936 cm−1 deg−2 for the skeletal torsional force constant.  相似文献   

3.
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 C2v 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.  相似文献   

4.
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 μA = 1.181(2), μB = 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.  相似文献   

5.
Microwave spectra of the trans-trans (TT) isomer of methylpropylether and its 12 isotopically substituted species were measured. The rs structure of this isomer was determined from the observed moments of inertia. Structural parameters of this isomer were roughly equal to those of the reported rs structures of trans-ethylmethylether and propane. Dipole moments of the TT isomer for the normal and two deuterated species were determined by Stark-effect measurements. For the normal species, the dipole moment was μa = 0.082 ± 0.010, μb = 1.104 ± 0.013, and μtotal = 1.107 ± 0.013 D making angles of 4°17′ with the b-inertial axis, of 6°7′ with the bisector of the COC angle. The barrier to internal rotation of the CH3C group was calculated to be 3300 ± 60 cal/mole from A-A splittings of the spectra in the CH3C excited torsional state.  相似文献   

6.
The microwave spectrum of tetrahydropyran-4-one has been studied in the frequency region 18 to 40 GHz. The rotational constants for the ground state and nine vibrationally excited states have been derived by fitting a-type R-branch transitions. The rotational constants for the ground state are (in MHz) A = 4566.882 ± 0.033, B = 2538.316 ± 0.003, C = 1805.878 ± 0.004. From information obtained from the gas-phase far-infrared spectrum and relative intensity measurements, these excited states are estimated to be ~ 100 cm?1 above the ground state for the first excited state of the ring-bending and ~ 185 cm?1 for the first excited state of the ring-twisting mode. Stark displacement measurements were made for several transitions and the dipole moment components determined by least-squares fitting of the displacements: (in Debye) |μa| = 1.693 (0.001), |μb| = 0.0, |μc| = 0.300 (0.013) yielding a total dipole moment μtot = 1.720 (0.003). A model calculation to reproduce the rotational parameters indicates that the data are consistent with the chair conformation.  相似文献   

7.
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 μa = 0.80(10), μb = 0.20(10), and μc = 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, Pcc, and rs 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.  相似文献   

8.
The rotational constants of four isotopic species of nitrogen trichloride have been obtained from transitions in the millimeter region. Two rs 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.  相似文献   

9.
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 μA 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(HcC) = 1.09 ± 0.015 Å, (HcCP) = 124.4 ± 0.8°; r(HtC) = 1.09 ± 0.015 Å, (HtCP) = 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 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   

10.
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   

11.
The microwave spectrum of 3,6-dioxabicyclo[3.1.0.]hexane has been obtained. The rotational lines of one ring conformation only have been observed and assigned. Ground state rotational constants are A0 = 6287.302 ± 0.011 MHa, B0 = 4683.546 ± 0.008 MHz, and C0 = 3358.517 ± 0.089 MHz. The diploe moment components obtained from Stark effect measurements are μa = 0.276 ± 0.010 D and μc = 2.47 ± 0.04 giving μ = 2.485 ±0.040 for the dipole moment of the molecule. The rotational constants and dipole moment components obtained experimentally can be satisfactorily explained only if the boat form is the most stable ring conformation.  相似文献   

12.
The spectrum of 1Δ and 3Σ SO has been studied in the millimeter and submillimeter region of the microwave spectrum. This expanded spectral coverage has made possible the measurement of twenty-two previously unobserved transitions, several of which are necessary for an accurate calculation of the energy levels. As a result, it is now possible to calculate the rotational transitions between energy levels for which J ≤ 10 in both the ground 3Σ electronic state and the excited 1Δ electronic state to an accuracy comparable to that of the microwave measurements themselves ( 1 MHz). Among the molecular constants calculated are; for the 1Δ state: B0 = 21 295.405 MHz, D0 = 0.0350 MHz, ωe = 1108 cm−1, and r0 = 1.4920 Å; and for the 3Σ state: B0 = 21 523.561 MHz, D0 = 0.03399 MHz, λ0 = 158 254.387 MHz, γ0 = −168.342 MHz, 0 = 0.305 MHz, r0 = 1.4840 Å, Be = 21 609.552 MHz, λe = 157 779.2 MHz, and re = 1.4811 Å.  相似文献   

13.
The microwave spectrum of 3-oxabicyclo(3.1.0.)hexane has been studied in the range 26.5–40 GHz (R-band) with a Hewlett Packard Model 8400 spectrometer. Both a and c-type R-branch transitions were used to derive the rotational constants for the ground state and first two excited states of the ring-puckering mode. The data are consistent with a single stable conformation, in agreement with a previous far-infrared study (1) and this is shown to be the boat conformation, as was the case with the similar molecules cyclopentene oxide (2, 3) (6-oxabicyclo(3.1.0.)hexane) and 3,6-dioxabicyclo(3.1.0.)hexane (1, 4). The rotational constants for the ground state are (in MHz) A = 6038.06; B = 4432.47; C = 3303.43 yielding κ = ? 0.174268. The electric dipole moment components of the ground state (in Debye units) are |μa| = 1.36 ± 0.02; |μc| = 1.03 ± 0.02 yielding a total dipole moment μ = 1.71 ± 0.03.  相似文献   

14.
Rabi oscillations were observed in the ASR(110), ΔM = 0 and ASQ(222), ΔM = 0 transitions of the ν2 band of 14NH3 in a molecular beam crossed by a CO2 laser beam. The frequency (in terms of the laser field amplitude) of the oscillations was used to determine the transition dipole moment of the ν2 band, yielding μsa = 0.261 ± 0.006 D. The hyperfine structure due to the electric quadrupole interaction of the nitrogen nucleus was clearly resolved.  相似文献   

15.
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 μa = 0.950 D, μb = 1.982 D, and μc = 1.135 D; μtotal = 2.67 D.  相似文献   

16.
The potential energy curve and theoretical dipole moment function of the a4Π state of NO have been determined using full-valence and first-order configuration interaction wavefunctions. Using these two different wavefunctions, the dipole moments of the a4Π, v = 3 level have been found equal, respectively, to 0.16 D and 0.30 D, with the polarity N+O. These values compare well with the value of |0.20 ± 0.04| D determined by Lisy and Klemperer. The first derivative of the dipole moment has also been calculated to be equal to 1.25–1.73 D/bohr.  相似文献   

17.
The ν1 fundamental band of FNO has been studied by the technique of CO laser Stark spectroscopy. The band origin was determined to be 1844.099 cm?1, and values for the rotational and centrifugal distortion constants of the (100) excited vibrational state were found. The ground state dipole moment components were determined to be μa = 1.690 and μb = 0.370 D, for a total dipole moment of 1.730 D, and a relatively large reduction (5%) was found in μ for the (100) state relative to the ground state.  相似文献   

18.
The rotational spectrum of 3-methylcyclopentanone has been observed in the frequency region from 18.0 to 26.5 GHz. Both a-type and b-type transitions in the ground vibrational state and a-type transitions in five excited states have been assigned. The ground state rotational constants are determined to be A = 5423.32 ± 0.18, B = 1949.51 ± 0.01, and C = 1529.59 ± 0.01 MHz. Analysis of the measured quadratic Stark effects gives the dipole moment components ∥μa∥ = 2.97 ± 0.02, ∥μb∥ = 1.00 ± 0.03, ∥μc∥ = 0.18 ± 0.06, and the total dipole moment ∥μt∥ = 3.14 ± 0.03 D. These data are consistent with a twisted-ring conformation with a methyl group in the equatorial position.  相似文献   

19.
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 KaKa = 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.  相似文献   

20.
Radiofrequency transitions withinK= 2 asymmetry doublets have been observed for the CO2–CO van der Waals complex. A Stark effect measurement on theJ= 2,K= 2 transition provides an electric dipole moment of μ = 0.2493(1) D. Combining this result with the permanent moment of CO, μCO= 0.1098 D, gives a change of moment on complex formation of Δμ = 0.140 D. The sign of Δμ is such that the CO end of the complex is more positive than CO2. The origin of Δμ should not be attributed to any single mechanism, and several different contributions to Δμ are discussed.  相似文献   

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