Rotational spectra, conformational structures and dipole moments of 2-(ethylthio)ethanol by jet-cooled FTMW and ab initio calculations

The rotational spectra of three low-energy conformers of 2-(ethylthio)ethanol also known as ethyl 2-hydroxyethylsulfide or hydroxyethyl ethyl sulfide (HOEES), together with the monosubstituted ¹³C and ³⁴S isotopic forms of the two lowest energy conformers, have been measured in a molecular beam using a pulsed-nozzle Fourier-transform microwave spectrometer. To search for the likely conformational structures, ab initio calculations were performed at the MP2/6-31G* level for reduced dimensionality potential energy mapping and at the MP2=FULL/6-311G** and B3LYP=FULL/6-311G** levels for full structural optimization and electronic energy calculations of possible lower energy conformers. In all, five low-energy conformers, each of C₁ point group symmetry, were located in the ab initio search with complete information obtained on rotational constants, dipole moments, and structures. Rotational constants for three of the conformers agree well with the experimental observations, leaving the other two with no experimental partners. The three having experimental matches display relatively open “chain-like” structures corresponding to TG-, and GG-like forms, while the two with no experimental matches display relatively closed or “folded” structures with significantly different rotational constants. Although results using different ab initio level theories with and without zero point energy corrections alter the conformer energy ordering slightly, the no-match conformers always stay in the lower energy group, leaving an unsolved question as to why these lower energy conformers with “folded-like” structures were not observed in the jet-cooled FTMW spectra.     

Description of nuclei in terms of their substructures

Applications of a microscopic approach of nuclear physics to an α+t+n+n+n+n cluster model of ¹¹Li and to a six-body treatment of ⁶Li are presented.     

The infrared spectrum of 31P14N near 1300 cm−1

The infrared absorption spectrum of the PN molecule has been measured at temperatures between 800 and 1050°C with a tunable diode laser. The transitions measured ranged from J″ = 3 to J″ = 53 and included the vibrational transitions v = 1 ← 0, 2 ← 1, 3 ← 2, and 4 ← 3. These measurements are combined with microwave measurements made by others to yield a consistent set of ten Dunham ro-vibrational constants and their uncertainties.     

Phase transitions in nuclear matter

The possible phases of nuclear matter are summarised. A new periodic phase of nuclear matter is discussed in details. In this phase the nucleon spin orientation follows the direction of the magnetic field associated with the periodic vector meson field. The probability of the transition accompanied by gamma radiation between this periodic phase and the anisotropic normal phase is derived.     

The microwave spectrum of a two-top peptide mimetic: the N-acetyl alanine methyl ester molecule

The rotational spectrum of N-acetyl alanine methyl ester, a derivative of the biomimetic, N-acetyl alanine N'-methyl amide or alanine dipeptide, has been measured using a mini Fourier transform spectrometer between 9 and 25 GHz as part of a project undertaken to determine the conformational structures of various peptide mimetics from the torsion-rotation parameters of low-barrier methyl tops. Torsion-rotation splittings from two of the three methyl tops capping the acetyl end of the -NH-C(=O)- and the methoxy end of -C(=O)-O- groups account for most of the observed lines. In addition to the AA state, two E states have been assigned and include an AE state having a torsional barrier of 396.45(7) cm(-1) (methoxy rotor) and an EA state having a barrier of 64.96(4) cm(-1) (acetyl rotor). The observed torsional barriers and rotational constants of alanine dipeptide and its methyl ester are compared with predictions from M?ller-Plesset second-order perturbation theory (MP2) and density functional theory (DFT) in an effort to explore systematic errors at the two levels of theory. After accounting for zero-point energy differences, the torsional barriers at the MP2/cc-pVTZ level are in excellent agreement with experiment for the acetyl and methoxy groups while DFT predictions range from 8% to 80% too high or low. DFT is found to consistently overestimate the overall molecular size while MP2 methods give structures that are undersized. Structural discrepancies of similar magnitude are evident in previous DFT results of crystalline peptides.     

Microwave spectrum of 1,2-propanediol

The microwave spectrum of the sugar alcohol 1,2-propanediol (CH₃CHOHCH₂OH) has been measured over the frequency range 6.5–25.0 GHz with several pulsed-beam Fourier-transform microwave spectrometers. Seven conformers of 1,2-propanediol have been assigned and ab initio electronic structure calculations of the 10 lowest energy forms have been calculated. Stark effect measurements were carried out on several of the lowest energy conformers to provide accurate determinations of the dipole moment components and assist in conformer assignment.     

Interstellar chemistry: a strategy for detecting polycyclic aromatic hydrocarbons in space

Polycyclic aromatic hydrocarbons (PAHs) have long been postulated as constituents of the interstellar gas and circumstellar disks. Observational infrared emission spectra have been plausibly interpreted in support of this hypothesis, but the small (or zero) dipole moments of planar, unsubstituted PAHs preclude their definitive radio astronomical identification. Polar PAHs, such as corannulene, thus represent important targets for radio astronomy because they offer the possibilities of confirming the existence of PAHs in space and revealing new insight into the chemistry of the interstellar medium. Toward this objective, the high-resolution rotational spectrum of corannulene has been obtained by Fourier transform microwave spectroscopy, and the dipole moment (2.07 D) of this exceptionally polar PAH has been measured by exploiting the Stark effect.     

Absolute alpha-decay width of212Po in a mixed shell-and-cluster model

We have reproduced the absolute width of theα decay of the ground state of²¹²Po in a model in which the shell model is combined with a²⁰⁸Pb+α cluster model, and found that the amount of core+α clustering in the parent state is ～30%.