Internal dynamics features in the free jet rotational spectrum of the acetaldehyde-Kr molecular complex

The structure and the dynamics of internal motions in the complex formed between acetaldehyde and Kr are studied by free jet absorption microwave spectroscopy performed in the range 60\u201378 GHz. The fourfold structure of each rotational line is evidence of the vibration-rotation coupling between the overall rotation of the complex, a tunneling motion of the Kr atom between two equivalent positions and the internal rotation of the methyl group in the acetaldehyde moiety. The four sets of transitions could be fitted with a coupled Hamiltonian which allows for the Coriolis interaction obtaining the energy separation between the vibrational energy levels related to the tunneling motion, while the observed splittings due to the methyl group internal rotation were analyzed independently with an appropriate model. The potential energy barriers for the tunneling motion and the internal rotation of the methyl group have been calculated and the interaction of the rare gas atom with the acetaldehyde moiety is reflected in the change of the V3 barrier to internal rotation in going from the molecule to the weakly bound complex

Internal motions of the rare gas atom in dimethyl ether-krypton

The free jet millimeter-wave absorption spectra of two isotopomers of the weakly bonded dimethyl ether-Kr complex have been assigned and measured. The Kr atom lies in the óV symmetry plane of dimethyl ether perpendicular to the COC plane, at a r0-distance of 3.67 Å from its center of mass (cm). The line connecting the krypton atom to cm forms an r0-angle of 70° with the O-cm line. The observed conformation is in agreement with the global minimum as found with a distributed polarizability model. Many rotational transitions are split into two component lines, due to the motion of Kr relative to dimethyl ether in the complex. The corresponding splitting has been used to determine the barrier to the internal motion. Information on the dissociation energy has been deduced from the centrifugal distortion effects

The millimeterwave free jet spectrum of vinyl acetate

The rotational spectrum of vinyl acetate has been assigned and measured by millimeter wave absorption free-jet spectroscopy. Only lines of the most stable conformer, the one with the carbonyl oxygen cis with respect to vinyl group and the terminal vinyl carbon trans with respect the acid group, have been observed. The observed species is the most stable one, according to theoretical calculations at the MP2(full)/6-311++G** level of theory. All rotational lines are split by internal rotation of the methyl group; the value of the barrier for this motion was determined to be V3 = 1.855(1) kJ mol-1

Interactions between organic molecules and water. Rotational spectrum of the 1:1 oxetane-water complex

The 1:1 molecular complex between oxetane and water has been investigated by using free-jet millimeter-wave spectroscopy. The rotational spectra of five isotopomers (with H2O, D2O, DOH, HOD and H218O) have been assigned. Partial r0 and rs structures of the complex have been derived. The water moiety lies in the plane of symmetry of oxetane, with the ™free∫ hydrogen E with respect to the ring. The oxetane ring appears to be slightly nonplanar, with the Cb carbon tilted on the opposite side of the water unity. The three atoms involved in the hydrogen bond adopt a linear arrangement with an Oring¥¥¥H distance of about 1.86 ä, and the angle between the COC bisector and the Oring¥¥¥H bond being ffi1068. Additionally, quantum-chemical calculations for the complex were performed and were found to be in agreement with the experimental results

Microwave spectrum of Salicylic Acid

The rotational spectra of salicylic acid and of three OD deuterated species have been investigated by free jet millimiter-wave absorption spectroscopy. Only lines of the most stable conformer, the one with an intramolecular hydrogen bond between the phenolic hydrogen and the carbonyl oxygen, have been observed. The positions of the phenolic and carboxylic hydrogens have been precisely derived

Morphing the internal dynamics of acetylacetone by CH3 → CF3 substitutions. the rotational spectrum of trifluoroacetylacetone

The rotational spectrum of trifluoroacetylacetone shows that the molecule exists in an enolic C(s) form and displays the features of internal rotations of the CH3 and CF3 groups, whose barriers to internal rotation were determined to be V3 = 379 and 30.8 cm(-1), respectively. Its internal dynamics appears to be intermediate between those of acetylacetone, where proton tunneling and low-barrier internal rotation of the two methyl groups make the spectrum quite complex, and hexafluoroacetylacetone, a perfectly "rigid" molecule on the time scale of microwave spectroscopy

Pyridine-CF4: A Molecule with a Rotating Cap

The rotational spectrum of pyridine-CF4 has been investigated by molecular beam Fourier transform microwave spectroscopy in a supersonic expansion. The CF4 moiety is located as a cap over the pyridine nitrogen, and the two parts are freely rotating with respect to each other. For this reason, in a first approximation, in the m = 0 state only the pyridine ring is rotating along the a-axis, and the value of rotational constant A' is nearly the same of the constant A of isolated pyridine. The (NCCF4)-C-..., distance is 3.372(1) angstrom. The dissociation energy has been estimated, from the centrifugal distortion, to be ca. 10 kJ/mol

Tunnelling rate and barrier to the transfer of the protic group in dimethylether–HCl

In dimethylether–HCl, the HCl group is tunnelling between the two lone pairs of the ether oxygen at a rate of 8182(7) MHz, through a barrier of 69 cm1, as deduced from the free jet millimetre wave absorption spectrum