Articles you may be interested inThe effects of two internal rotations in the microwave spectrum of ethyl methyl ketone Centrifugal distortion and internal rotation analysis of the microwave spectrum of ethyl fluoride J. Chem. Phys. 78, 3541 (1983); 10.1063/1.445177 Microwave spectrum and rotational isomerism of ethyl nitrateThe microwave torsional-rotational spectra of several species of gauche ethyl alcohol have been assigned and analyzed. The species studied are CH 3 CH 2 0H, CH 3 CHPD, CH 2 DCH 2 0H, and CH 2 DCH 2 0D, both methyl symmetric and asymmetric forms of the last two species. Rotational coefficients have been determined for all species. For the normal species, the components of the dipole moment have been determined as lu.1 = 1.264±0.01O D, lubl = 0.104±0.OO8 D, and lucl = 1.101 ±0.016 D. The tunneling frequency between the two gauche substrates is measured to be .d = 96739.3 MHz and the gauche-trans energy difference is measured to be 41.2±5.0 cm-I for the normal species. The first three coefficients in the Fourier expansion of the hydroxyl internal rotation potential energy are determined to be VI = 57.0 cm-I , V 2 = 0.8 cm-I , and V3 == 395.0 cm-I . The barrier to methyl internal rotation for gauche CH 3 CH 3 0H is The barrier to methyl internal rotation for gauche CH 3 CHPH is determined to be V3 = 1331 cm -I. Analysis of the interaction between methyl and hydroxyl internal rotations for CH 2 DCH 2 0H and CH 2 DCH 2 0D determine, for -OH: V,1s2 = 8±2 cm-I ; and for -OD: V,b2 = 4±1 cm -I for the coefficient of sina I sina2 in the effective internal rotation potential energy for these low symmetry species.

The microwave absorption spectrum of C6H5CHO has been investigated in the region 17.5–40.0 GHz and that for C6H5CDO in the region 26.5–40.0 GHz. Rotational transitions in the ground and first three excited torsional states in both molecular species have been identified. There is evidence for interaction of the second torsional state of C6H5CHO with another mode of vibration of the molecule. Accurate relative intensity measurements give the first torsional frequency of 113.8 ± 5.0 cm−1 for C6H5CHO and of 108.4 ± 4.25 cm−1 for C6H5CDO. The barriers to internal rotation of the aldehyde group calculated from these frequencies are 4.90 ± 0.43 and 5.28 ± 0.42 kcal/mole for C6H5CHO and C6H5CDO, respectively. The discrepancy between the observed and calculated values of inertial coefficients suggests the importance of vibration–rotation interaction in the theory of internal rotors with twofold potential barriers.

The microwave spectrum of the trans and gauche isomers of the normal and two isotopic species (CH3CH2SD and CH2DCH2SH) of ethyl mercaptan has been studied. Identification of the spectrum of the trans isomer of the normal and sym-CH2DCH2SH molecules has been extended up to J=19, enabling preliminary centrifugal distortion constants to be determined. From a and c dipole transitions full sets of rotational constants of the gauche isomer of all species have been determined. For the normal molecule they are A=28 746.37 MHz, B=5294.85 MHz, and C=4846.96 MHz. The tunneling frequency of the thiol top between its two equivalent gauche configurations has been measured directly for the normal species (1754.09 MHz), sym-CH2DCH2SH (1790.05 MHz), and CH3CH2SD (70.40 MHz). Identification has been made of excited thiol torsion satellites in both isomers. Dipole moments of all configurations for each species have been determined using second-order Stark effects. For the trans isomer of the normal molecule they are μa=1.06±0.03 D, μb=1.17±0.03 D,μc=0, μ=1.58±0.04 D; for the gauche isomer of the normal molecule they are μa=1.48±0.02 D, μb=0.19±0.10 D, μc=0.59±0.02 D, μ=1.61±0.05 D. An approximate structure, which has been fit to the data, indicates that the thiol top rotates about an axis with the CS bond tilted away from the axis by 3.16 °±0.05 °, while & CSH=95.23 °±0.50 ° and the angle of the axis with the CC bond is 111.71 °±0.10 °. The barrier to methyl internal rotation in the trans isomer was found to be 1156±30 cm−1. Splittings observed in the gauche ground state of the normal and sym-CH2DCH2SH molecules have been effectively reproduced on the basis of structural effects and tunneling. Relative intensity measurements show the gauche isomer to be lower in energy with the difference between the lowest states (trans − gauche) equal to 142±15 cm−1 for the normal species and 138±30 cm−1 for CH3CH2SD. Using the measured energy differences of the ground and excited states, the first three Fourier coefficients of the thiol torsional potential were found to be V1 = −65 cm−1, V2 = −135 cm−1, and V3 = 440 cm−1. Evidence of coupling between the methyl and thiol internal rotors was also investigated.

No abstract

No abstract