RESUMEN
An internal axis method (IAM) has been used to determine the potential energy coefficients V(1), V(2), and V(3) to internal rotation in CH(2)DSH and CHD(2)SH. Two torsional differences for the gauche ground states and one torsional difference for the excited states were used to fix the V's. A fourth term, K(varsigma), 3(e(2))-2(o(2)), determines the torsional state assignment for this Q-branch series as o(2) to e(2) that was not known previously. For CH(2)DSH, the potential energy coefficients are V(1) = 4.54 cm(-1), V(2) = -9.36 cm(-1), V(3) = 440.50 cm(-1); for CHD(2)SH, V(1) = -4.12 cm(-1), V(2) = 8.23 cm(-1), V(3) = 439.65 cm(-1). Nonrigidity coefficients have also been determined for both the trans and gauche conformations of the ground state. Copyright 2001 Academic Press.
RESUMEN
The microwave torsional-rotational spectra of gauche CH(3)CD(2)OH and CH(3)CD(2)OD have been identified, assigned, and analyzed up to 70 GHz. From the observed a- and c-dipole transitions, it has been possible to determine the effective rotational coefficients and the gauche tunneling energy of the hydroxyl internal rotation. The product of inertia terms I(xy) and I(xz) were included in the analyses using the framework fixed axis method (FFAM) approach to the hydroxyl internal rotation. Further, the analyses were sensitive to selected effective centrifugal distortion coefficients. For CH(3)CD(2)OH, a-dipole lines were assigned for the first excited gauche state. As for CH(3)CH(2)OH, these lines were highly nonrigid rotor in behavior more than likely due to the resonance with the first excited state of the methyl torsion. Copyright 2000 Academic Press.
RESUMEN
The zeroth-order kinetic energy is developed for the vibrating-rotating-internally rotating CH(2)DOH and CHD(2)OH molecules using the general theory of Guan and Quade for the vibration-rotation-large amplitude internal motion interactions in molecules. A T transformation is applied to obtain the necessary (G(-1))(0) vibrational matrix elements in the kinetic energy for the R transformation that separates the internal rotation from the 3N-7 other vibrations. Then, a second T transformation is used to separate rotation from the 3N-7 other vibrations in zeroth order in the kinetic energy. The overall rotation and internal rotation remain coupled in zeroth order. All zeroth-order kinetic energy coefficients are calculated from the molecular structure and masses for the methyl alcohol molecules. The physical significance of the transformations is discussed in detail. This paper reports the results of the first segment of the three segments that are necessary in the calculation of the full solution to the problem. Copyright 1999 Academic Press.
RESUMEN
Previously identified, measured, and rotationally assigned but unpublished J = 0-1 and 1-2 microwave a-dipole lines for excited states of the torsion for CH2DOH and CHD2OH are given torsional assignments for the first four excited states. The troublesome assignments were for the K-1 = 0 lines of the o2 state of CH2DOH and the e2 state of CHD2OH, where a resonance is found for the J0J levels. The assignment for these states was facilitated by combination differences with the b- or c-dipole intratorsional state transitions, relative intensities, and FIR combination differences for the e2 and e3 states of CH2DOH. A few new b- and c-dipole assignments are reported for o2 of CH2DOH and e2 of CHD2OH. Transitions for these two states have been analyzed to estimate the strength of the resonant interaction and energy difference for the levels involved and to estimate how well the theory is predicting the K-1-dependent torsional energy levels. The empirically determined DeltaB and DeltaC from nonrigidity for each species for the four excited states should prove helpful for future calculations of vibration-internal rotation-overall rotation interactions in these molecules. Copyright 1998 Academic Press.
RESUMEN
The zeroth order kinetic energy is developed for the vibrating-internally rotating-rotating CH3OH molecule using the general theory of Guan and Quade for large amplitude internal motion-vibration-rotation interactions in molecules. The R and T transformations are applied, respectively, to separate internal rotation from the other vibrations and overall rotation from the other vibrations in zeroth order. All zeroth order kinetic energy coefficients are calculated from the geometry and atomic masses of the CH3OH molecule. The physical significance of the two transformations is discussed in detail. This paper reports the results of the first segment of the many segments necessary in the calculations for full solution of the problem. Copyright 1998 Academic Press.
RESUMEN
Previous studies of the microwave rotational spectra of gauche CH2DCH2OH have been extended for the torsional ground state and new studies are reported for the first excited states of the -OH torsion. The extended studies for the ground state hydroxyl gauche, methyl symmetric conformation made it possible to determine the product of inertia coefficients D and E as well as the rigid rotor A, B, and C and the centrifugal distortion coefficients DeltaJ and DeltaJK. Likewise for the hydroxyl gauche, methyl asymmetric conformations I and II in the ground state rotational coefficients and selected centrifugal distortion coefficients have been determined. Rotational coefficients B and C and centrifugal distortion coefficients DeltaJ and DeltaJK have been determined for all of the excited states. A significant result of the spectroscopic search was that c-dipole transitions were not observed within the range of our spectrometer for either the methyl symmetric or methyl asymmetric conformations in the excited states. For the methyl asymmetric conformation, this means that the tunnelling energy for the excited state has overcome the torsional potential energy term that suppressed the pure hydroxyl tunnelling, that localizes the molecule into conformations I and II for the ground state. The very small tunnelling energy within conformations I and II has been predicted. The role of internal rotation-overall rotation Coriolis coupling including denominator corrections from the rotational energy for hydroxyl gauche, methyl symmetric CH2DCH2OH is shown in the Appendix to contribute to the effective rotational coefficients. Copyright 1998 Academic Press.
RESUMEN
Fourier transform microwave (FTMW) spectroscopy has been used to observe and resolve the 60-kHz tunneling splitting between the symmetric and antisymmetric substates of conformations I and II for hydroxyl gauche, methyl asymmetric CH2DCH2OH. Conformation I has the hydroxyl H and methyl D on the same side of the molecular plane whereas conformation II has them on the opposite sides. The determination of the small energy difference between these two conformers leads to an improved value of Vs1s2, (the potential energy coefficient that localizes the molecule into conformations I and II) of 4.8(5) cm-1. Further, the relative intensities of the spectra show that conformation II is lower in energy than conformation I. Analysis of the quadrupole splittings of the a-type 101-000 transitions determines values for eQqaa that range from -87 to -98 kHz for both hydroxyl conformations with the methyl group asymmetric and +84 to +102 kHz for both hydroxyl conformations with the methyl group symmetric. Copyright 1998 Academic Press.
RESUMEN
The theory of vibration-rotation interactions in polyatomic molecules using curvilinear internal coordinates for the vibrational degrees of freedom is extended to the situation where the initial molecular axis system is not the principal axis system of the equilibrium configuration. For this new situation, the transformation coefficient rhoit is derived as well as the vibrational coefficients (G-1tt')0. This new transformation may not be useful nor necessary when all of the internal motions are of small amplitude. However, in the case of vibration-rotation-internal rotation interactions, the new transformation is helpful when the internal rotor is a symmetric top and necessary when the internal rotor is an asymmetric top. Copyright 1998 Academic Press. Copyright 1998Academic Press