The Ground and First Excited Torsional States of Acetic Acid.

A global fit of microwave and millimeter-wave rotational transitions in the ground and first excited torsional states (v(t) = 0 and 1) of acetic acid (CH(3)COOH) is reported, which combines older measurements from the literature with new measurements from Kharkov, Lille, and NIST. The fit uses a model developed initially for acetaldehyde and methanol-type internal rotor molecules. It requires 34 parameters to achieve a unitless weighted standard deviation of 0.

Infrared and Millimeter-Wave Study of the Four Lowest Torsional States of CH(3)CF(3).

An investigation of the torsion-rotation Hamiltonian of CH(3)CF(3) in the ground vibrational state has been carried out using infrared and mm-wave spectroscopy. With infrared Fourier transform spectroscopy, the weak, torsional overtone (v(6) = 2 <-- 0) has been studied leading to the measurement of 382 frequencies between 405 and 440 cm(-1) at a resolution of 0.005 cm(-1).

Millimeter-Wave Spectrum of CF(2)Cl(2), Taking into Account the Hyperfine Structure.

A new investigation of the CF(2)(35)Cl(2) ground state rotational spectrum in the 50-100 GHz frequency range gave an opportunity to improve the accuracy of rotational and quartic distortion parameters by an order of magnitude and to determine values of six sextic centrifugal distortion parameters. A special technique was used to process line profiles of unresolved or partially resolved hyperfine structures of rotational transitions. It allowed us to improve significantly values for the diagonal parameters of quadrupole coupling chi(aa), (chi(bb)-chi(cc)) and to determine the off-diagonal parameter chi(ab).

Microwave Spectroscopy of the Ground, nu18, 2nu18, and nu11 Vibrational States of CF3CFH2.

The rotational spectra of the ground, nu18, 2nu18, and nu11 vibrational states of CF3CFH2 have been investigated in the frequency range 48-116 GHz with an accuracy of measurement better than 10 kHz. Rotational and centrifugal distortion parameters derived using an S-reduced Watson-type Hamiltonian have been improved for the ground and nu18 states. An interaction between 2nu18 and nu11 vibrational states has been detected, and rotational, centrifugal distortion, and coupling parameters of these states have been determined for the first time.