N. Heineking

Molecular structure of iodoacetylene

Abstract The pure rotational spectra of iodoacetylene and its [1-13C]-, [2-13C]-, and [D]-isotopomers have been assigned. From the set of four rotational constants obtained, the r0-structure and the partial rs-structure of the ethynyl moiety have been determined. From the hyperfine structures the nuclear quadrupole and spin-rotation coupling constants of iodine have also been measured.

The microwave spectrum of tert-butyl isocyanate

Abstract The rotational spectrum of tert-butyl isocyanate, (CH3)3C-NCO, has been assigned using pulsed molecular beam microwave Fourier transform spectroscopy. The rotational constants are A = 4572.6 MHz (assumed), B = 1632.948 (15) MHz, C = 1630.493 (14) MHz; the barrier to internal rotation of the tert-butyl group (assumed to constitute a symmetric internal rotor, the NCO group forming the frame) is V3 = 41.510 (15) cm−1, the moment of inertia of the internal top is I α = 111.388 (4) amu · A 2 , and the angle between the internal rotor axis and the a-principal inertia axis is θ = 24.169 (3)°. The nitrogen nuclear quadrupole coupling constants are χaa = +2.6376 (4) MHz, χbb = −1.4935 (7) MHz, χcc = −1.1441 (7) MHz, χac = +0.1731 (15) MHz (the molecule has an ac-plane of symmetry). The principal elements of the coupling tensor are χzz = +2.6455 MHz, χxx = −1.4935 MHz, χyy = −1.1520 MHz; the angle between both axis systems is 〈(az) = +2.615° (with the x-axis perpendicular to the symmetry plane).

Nuclear quadrupole hyperfine structure in the l-type spectra of chloro-, deuterochloro-, and bromoacetylene in the v5 = 11 vibrational states

The l-type doublets of the J = 2-1 rotational transitions of chloroacetylene, deuterochloroacetylene, and bromoacetylene in the v5 = 11 states have been accurately remeasured and analyzed. Based on the results, direct l-type transitions in the frequency range 4–12 GHz have been assigned for the first time. All transitions showed halogen nuclear quadrupole hyperfine structure. For bromoacetylene, an asymmetry in the spin-rotation coupling of bromine has been detected.

A Molecular Beam Microwave Fourier Transform (MB-MWFT) Spectrometer with an Electric Discharge Nozzle

Abstract We report on first experiments with our pulsed molecular beam microwave Fourier transform (MB-MWFT) spectrometer using a special nozzle which allows high voltage discharges within the nozzle orifice. Under these conditions we observed low J rotational transitions in highly excited vibrational states of carbonyl sulfide and sulfur dioxide, and also rotational lines of the SO radical in the 3Σ- electronic ground state and both the vibrational ground and first excited state.

The Microwave Spectrum of 4-Methylisothiazole

The microwave spectrum of 4-methylisothiazole was assigned by means of a pulsed molecular beam microwave Fourier transform spectrometer. Analysis of the spectrum yielded the rotational constants .4 = 7370.642(31) MHz, B = 2515.8461 (30) MHz, C = 1897.2863(33) MHz, a threefold barrier to internal rotation of the methyl group of V3 = 3170.81 (130) GHz≙ 105.7669(430) cm-1, a momentum of inertia of the methyl group of Iα = 3.16769(130) amu · Å2 and an angle between internal rotor axis and principal a-axis of Θ= 5.406(38)°. The nitrogen quadrupole coupling constants were determined to be χ+ = χbb + χcc = 1.4822(14) MHz, χ -= χbb-χcc = - 1.4353(25) MHz and χab= - 3.16(12) MHz.

The hyperfine structure of germyl chloride

The J = 1−0 and J = 2−1 transitions of germyl chloride GeH3Cl have been investigated by microwave Fourier transform spectroscopy (MWFT) for all the isotopic species of germanium and chlorine. The quandrupole and spin-rotation coupling constants of 35Cl, 37Cl, and 73Ge have been determined very accurately for the first time.

The Effect of Deuteration on the Molecular Dipole Moments of Haloacetylenes

Abstract The dipole moments of chloro-, bromo-, and iodoacetylene, and those of the respective deuterated species, have been accurately determined using microwave Fourier transform spectrometers equipped with Stark cells. In each case, deuteration resulted in a change of the value of the dipole moment of about 0.012 D. The results provide strong evidence that the orientation of the dipole moment vector of iodoacetylene is opposite to that of the other haloacetylenes.

Radiofrequency Microwave Double Resonance Experiments in Fourier Transform Technique

Abstract Radiofrequency microwave double resonance has proved as a valuable method in microwave spectroscopy in the frequency domain. We present comparable experiments in the time domain Fourier transform spectroscopy.

14N Nuclear Quadrupole Coupling Constants of Acetamide and α-Fluoroacetamide

Abstract The 14N nuclear quadrupole hyperfine structures in the rotational spectra of acetamide, CH3CONH2 , and α-fluoroacetamide, FCH2CONH2 , have been resolved. From the observed patterns, the quadrupole coupling constants have been determined with high precision. The results provide evidence of considerable derealization of the nitrogen lone electron pair. For acetamide, the full coupling tensor has been determined from a combined analysis of the ground and first excited state of the methyl group internal rotation. The spectrum of α-fluoroacetamide-[15N] has been obtained for the first time, and a refined structure is proposed.

Bromine Spin-Rotation Coupling Constants of Cyclopropylbromide-79Br and -81Br

Abstract We reinvestigated the microwave spectrum of cyclopropylbromide with the increased resolution of pulsed microwave Fourier transform spectroscopy. Because of the higher frequency precision, it was possible to determine the spin-rotation coupling constants of bromine. Global fits of rotational constants, quartic centrifugal distortion constants, quadrupole coupling constants including the off-diagonal component χac , and spin-rotation coupling constants simultaneously to almost one hundred hyperfine components for each of the two bromine isotopomers resulted in overall standard deviations of well below 5 kHz