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1.
Rotational transitions of CH3CCSiH3 have been observed in the millimeter-wave region using a computer-controlled source-frequency modulation spectrometer with a 1.8-m-long free space absorption cell. The observed spectrum clearly showed the effect of internal rotation with a small potential barrier. It has been analyzed by calculating the torsion-rotation energies on the basis of torsional wave functions obtained by diagonalizing the torsional part of the Hamiltonian. The least-squares analysis has yielded the rotational constant B = 2068.2817(4) MHz and a few centrifugal distortion constants. The barrier height to internal rotation has been determined to be 3.77(70) cm?1 from the contour map of the standard deviation. Also, the A rotational constant of the silyl group around the symmetry axis has been estimated by fixing the A constant of the methyl group to the value of CH3CCH.  相似文献   

2.
High-resolution Fourier transform spectra of CH3OH have been investigated in the infrared region from 930 to 1450 cm−1 in order to map the torsion-rotation energy manifolds associated with the ν7 in-plane CH3 rock, the ν11 out-of-plane CH3 rock, and the ν6 OH bend. Upper-state term values have been determined from the assigned spectral subbands, and have been fitted to power-series expansions to obtain substate origins and effective B-values for the three modes. The substate origins have been grouped into related families according to systematic trends observed in the torsion-vibration energy map, but there are substantial differences from the traditional torsional patterns. There appears to be significant torsion-mediated spectral mixing, and a variety of “forbidden” torsional combination subbands with |Δυt|>1 have been observed, where υt denotes the torsional quantum number (equivalent to υ12). For example, coupling of the (υ6,υt)=(1,0) OH bend to nearby torsionally excited (υ7,υt)=(1,1) CH3-rock and (υ8,υt)=(1,1) CO-stretch states introduces (υ6,υt)=(1,0)←(0,1) subbands into the spectrum and makes the ν7+ν12ν12 torsional hot band stronger than the ν7 fundamental. The results suggest a picture of strong coupling among the OH-bending, CH3-rocking, and CO-stretching modes that significantly modifies the traditional energy structure and raises interesting and provocative questions about the torsion-vibration identity of a number of the observed states.  相似文献   

3.
Infrared intensity analysis was done in two ways. In one approach, formulas connecting electrooptical parameters (eop's) and intensities were derived and, using the intensities, the former were obtained. In evaluating the eop's the intensity sum equations were used directly so that the sign ambiguity of δPδQ is avoided. In the other method, polar tensors were obtained directly from intensities. The two methods have now been connected, and polar tensors have been obtained in terms of electrooptical parameters so that the former were also free from sign ambiguity of δPδQ. They compare well with those obtained directly from intensities. In similar connecting formulas by other authors [see, for example, P. L. Prasad, J. Chem. Phys., 69, 4403, (1978)], both polar tensors and eop's were affected by the sign ambiguity.  相似文献   

4.
We obtained twelve new far infrared laser transitions by optically pumping the CH2DOH, CH3I, CD3I and Trioxymethylene molecules with a CW CO2 laser having a tunability range of 280 MHz. We measured the wavelength, polarization, relative intensity and pump offset relative to the CO2 center frequency for all the new lines.  相似文献   

5.
The pure rotational spectrum driven by the small dipole moment produced perpendicular to the symmetry axis by centrifugal distortion has been investigated for CH3SiF3 in the ground vibrational state using a Fourier transform waveguide spectrometer. Between 10.9 and 17.0 GHz, four (k + 3 ← k) series in the Q branch have been measured in the lowest torsional state v6 = 0 for k = 4, 5, 6, and 7 with 54 ? J ? 65. In each transition, the quantum number σ = 0, +1, −1 labelling the different torsional sub-levels is conserved. For given (J,k), splittings from ∼10 to ∼45 MHz have been observed between lines with different values of σ. The global data set includes the anticrossing molecular beam energy differences of [W.L. Meerts, I. Ozier, Chem. Phys. 71 (1982) 401-415] as well as the mm-wave R branch frequencies and (A1 − A2) splittings of [P. Dréan, J.-M. Colmont, J. Demaison, L. Dore, C. Degli Esposti, J. Mol. Spectrosc. 176 (1996) 23-27]). A good fit was obtained by varying 15 molecular parameters characterizing the torsion-rotation Hamiltonian HTR for the vibrational ground state. Because of the strong correlation between two of the quartic torsion-distortion parameters (F0,3K and D0,Km) and a redundancy connecting the centrifugal distortion constants, four models were obtained yielding comparable fits. In each case, effective values were determined for the A-rotational constant and the height of the potential hindering the internal rotation. A high precision determination of the structural parameter ρ was made that is the same in all four models. For the off-diagonal quartic centrifugal distortion constant ε0 and the sextic constants H0,J, H0,JK, H0,KJ, and h0,3, the differences in the values obtained in the two different reductions used have been explained in terms of the redundancy connecting these parameters. For σ = 0, +1, −1, the energy level pattern for (|k| = 3) is discussed for the case where the pure torsional energy splitting and the matrix elements off-diagonal in k are of comparable magnitude. A method is described of using an R branch study of the resulting σ-splittings for (|k| = 3) to probe the zeroth-order torsional Hamiltonian.  相似文献   

6.
The JJ + 1 transitions (J = 4, 5, 6, 7, 8) in the microwave spectra of methyl isocyanide and its 15N derivative have been obtained and analyzed in the 4ν8 degenerate vibrational state. Theoretical analytical expressions are given for the rotational frequencies in a 4νE state, separately for the l = 0, ±2, ±4 values. These formulas could only be used as a starting point for the assignment and analysis, because of the complexity of the spectrum and the number of accidental resonances appearing in many l = 0 and ±2 lines for low K values. A detailed analysis was obtained through a diagonalization of the energy matrix. Many types of A1A2 doublings could be localized; in particular for CH315NC the K, l = ±1, ±4 doubling allowed the calculation of the g6 coefficient of the 〈K, l|H|, l ± 6〉 term. As in the 3ν8 state, some lines seem to undergo the effects of a vibrational resonance. A set of constants is given for both species, and a comparison is made with the other states.  相似文献   

7.
In order to provide accurate rest frequencies for astronomical searches, the spectrum of perdeuterated methanol, CD3OD, has been measured in the frequency range 62-233 GHz. A total of 379 lines was measured from rotational states up to J=20 and K=10 within the ground and first excited torsional states (vt=0 and 1). Using a one-dimensional torsion-rotation Hamiltonian, the lines were fitted to measurement accuracy (<30 kHz).  相似文献   

8.
Eight rotational transitions of the complex (CH3)3CCN-SO3 have been recorded using pulsed-nozzle Fourier transform microwave spectroscopy and a series of ab initio calculations has been performed. The complex is a symmetric top with free or nearly free internal rotation of the SO3 and (CH3)3CCN subunits. The nitrogen-sulfur bond distance is determined to be 2.394(19) Å. Calculations at the MP2/aug-cc-pVTZ level/basis, which are in excellent agreement with the experimental results, give a binding energy of 11.0 kcal/mol relative to (CH3)3CCN and SO3. Physical properties of the system, including N-S bond length, N-S-O angle, binding energy, and the degree of electron transfer (obtained from Townes and Dailey analysis of the 14N nuclear quadrupole coupling constant) are compared with those of similar complexes. The proton affinity of the base is a useful parameter for ordering complexes in the series.  相似文献   

9.
The regions around the respective carbon, nitrogen and oxygen K-edges of CH4, NH3, H2O, CH3OH, CH3OCH3 and CH3NH2 have been investigated by electron energy loss spectroscopy using a beam of 2.5 keV electrons. All spectra show a number of discrete peaks just below the K-shell ionization threshold. These discrete structures have been interpreted as being associated with the promotion of a K-shell electron to Rydberg orbitals which converge to the K-shell ionization threshold.  相似文献   

10.
The problem of attaching K rotational quantum number labels after the second diagonalization step in the ρ-axis-method treatment of methyl-top internal rotation problems is considered. A new partially computer-automated labeling scheme for K-labeling is proposed. The scheme is rather simple and does not require any information other than that provided by the numerical eigenvectors obtained after diagonalization of the torsion-rotation Hamiltonian matrix. It assumes that within a given K stack, torsion-rotation eigenfunctions vary slowly when J changes by unity. The basic idea is thus to search for similarities in basis-set composition in torsion-rotation eigenvectors belonging to adjacent J values. In such a way, torsion-rotation states of adjacent J values having the same value of K are connected. This allows one to transfer a given K-label from lower J values, where it can be determined easily (either from eigenvector composition or from energy-ordering considerations), to higher J values, which are characterized by extensive basis-set mixing. The approach was successfully applied to the K-labeling problem of prolate (acetaldehyde, methanol, and ethyl acetamidoacetate) and oblate (acetic acid, acetamide) rotors characterized by significant torsion-rotation interactions in their spectra. The scheme gives correct K-labels for eigenvectors in the majority of cases. The problems with the remaining cases are mainly caused by localized avoided crossing interactions, which can be fixed relatively easily in manual mode using a graphical visualization of the torsion-rotation energy level diagram.  相似文献   

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