A. Bauder

The microwave spectrum and dipole moment of azulene

Abstract The microwave spectrum of azulene (C 10 H 8 ) has been investigated in the frequency region 7–13 GHz. Rotational transitions for the ground state and one excited vibrational state could be assigned and the following rotational constants have been determined for the ground state: A = 2841.951 ± 0.024 MHz, B = 1254.8463 ± 0.0010 MHz, and C = 870.7162 ± 0.0008 MHz; and for the exeited state: A = 2841.73 ± 0.22 MHz, B = 1254.771 ± 0.008 MHz, and C = 871.478 ± 0.007 MHz. The Stark effect of four ground-state rotational transitions has been analyzed and the dipole moment has been determined to be 0.796 ± 0.014 D lying only in the a axis. Evidence is given for C 2 v symmetry of azulene considering Stark effects and inertial defects.

Exact quadrupole interaction energies in rotational spectra

Abstract The quadrupole hyperfine interaction energies in rotational spectra have been calculated through exact diagonalization of the total Hamiltonian matrix composed of the rotational and the quadrupole interaction part. Group-theoretical methods (Wigner-Eckart theorem) have been used extensively to calculate the matrix elements directly in the appropriate coupled representation. Thus, it is possible to evaluate the correct intensities of the individual hyperfine transitions. A computer program has been written to perform these calculations and some examples are given.

Microwave spectrum, centrifugal distortion analysis, and harmonic force field of nitric acid

Abstract The assignment of rotational transitions of nitric acid was extended up to J = 74 between 18 and 40 GHz. The newly measured transition frequencies were combined with previously reported transition frequencies in order to adjust all three rotational constants, five quartic, and seven sextic distortion constants in a least-squares fit: B a = 13011.025(5) MHz, B b = 12099.855(5) MHz, B c = 6260.641(5) MHz, Δ j = 14.00(3) kHz, Δ JK = − 20.168(4) kHz, Δ K = 7.44(1) kHz, δ J = −1.1820(2) kHz, δ K = 20.566(5) kHz, Φ J = −0.16(4) Hz, Φ JK = −0.086(4) Hz, Φ KJ = 0.052(13) Hz, Φ K = 0.11(3) Hz, ϕ J = 0.00952(6) Hz, ϕ JK = 0.135(3) Hz ϕ K = −1.14(3) Hz (oblate III r representation). An improved harmonic force field of nitric acid was obtained from ab initio calculations which were appropriately scaled in order to reproduce the observed vibrational frequencies. The quartic centrifugal distortion constants calculated from this harmonic force field are in good agreement with those obtained from microwave observations.

Microwave spectrum, quadrupole coupling constants, and dipole moment of nitroethylene

Abstract The microwave spectrum of nitroethylene (CH 2 CHNO 2 ) and one deuterated species (CH 2 CDNO 2 ) has been investigated in the region from 8 to 26 Gc/sec. High resolution spectra have been run to find the nitrogen hyperfine splittings. A numerical analysis of the spectra yielded the following rotational and quadrupole coupling constants of the normal species in the ground vibrational state: A = 11 811.757 ± 0.010 Mc/sec, B = 4 680.7851 ± 0.0021 Mc/sec, C = 3 353.7697 ± 0.0025 Mc/sec, χ aa = −883 ± 49 kc/sec, χ bb = 14 ± 24 kc/sec, and χ cc = 869 ± 49 kc/sec. The ground-state rotational constants for the deuterated molecule were found to be A = 11 042.68 ± 0.04 Mc/sec, B = 4 658.475 ± 0.015 Mc/sec, and C = 3 278.069 ± 0.015 Mc/sec. The dipole moment of 3.70 ± 0.03 D was determined from Stark displacements. Relative intensity measurements of satellites arising from excited states of the torsional motion of the nitro-group led to an estimate of 100 ± 20 cm −1 for the torsional transition frequency. Finally, it is shown that nitroethylene has a planar molecular structure.

Microwave spectrum, dipole moment and barrier to internal rotation of peroxyacetic acid

Abstract The microwave spectra of peroxyacetic acid (CH 3 COOOH) and a deuterated form (CH 3 COOOD) have been investigated in the frequency range from 12 to 40 GHz. The assigned transitions have been analyzed by numerically diagonalizing the hamiltonian for the overall rotation and internal rotation of a semirigid model. A threefold barrier for the methyl top of 76.70(45)cm −1 has been obtained. From the Stark effect, the dipole moment has been determined to be μ a = 2.294(3) D, μ b = 0.650(4) D and μ total = 2.384(5) D. The measured moments of inertia suggest a planar structure for the peroxy acid group.

The microwave spectrum and dipole moment of heptafulvene

Abstract The microwave spectrum of heptafulvene (C 8 H 8 ) has been investigated in the frequency range from 26 to 40 GHz. The following rotational constants have been obtained from a least-squares fit of the measured transition frequencies: A = 3665.972(66)MHz, B = 2004.3165(59)MHz, and C = 1297.5029(90)MHz. From the corresponding moments of inertia it was concluded that heptafulvene has a planar equilibrium structure. The quantitative measurement of the Stark splittings of three transitions have yielded a dipole moment of 0.477(5) D along the a principal axis. A series of satellite transitions accompanied each rotational transition. The satellites have been assigned to the lowest out-of-plane vibration ν 42 (B 2 ) for which a frequency of 70(11) cm −1 has been determined from relative intensity measurements.

Microwave spectra, substitution structure and vibrational satellites of formic anhydride

Abstract The microwave spectra of all singly substituted D, 13 C and 18 O species and a few doubly substituted species of formic anhydride have been analyzed. The complete substitution structure has been determined from these data. Vibrational satellites for the three lowest normal modes have been identified. From relative intensity measurements the following normal frequencies have been deduced: ν 15 (a″) = 85 + 8 cm −1 , ν 14 (a″) = 211 ± 10 cm −1 and ν 11 (a′) = 236 + 20 cm −1 .

Linear reactor-infrared matrix and microwave spectroscopy of the gas phase ethylene ozonolysis

Abstract Investigation of the gas phase reaction of ethylene with ozone by means of two novel experimental techniques — combination of the linear reactor with

Barrier to internal rotation of dimethyl ether: ab initio SCF study including structure relaxation and comparison to experimental results

Abstract Ab initio SCF quantum chemical calculations have been performed for four different conformations of the methyl groups in dimethyl ether. The structure was allowed to relax during internal rotation of the methyl tops. The structural parameters of the frame have been optimized for the four conformations. A considerable variation of 3.7° was found for the COC angle during internal rotation of both methyl tops. The quantum chemical barriers to internal rotation have been compared with recent microwave and infrared and Raman investigations. In addition, structural parameters, potential energy and electric dipole moment components are reported as functions of the internal rotation angles.

Modulation techniques for broadband microwave-microwave double resonance spectrometers

The operation of a microwave-microwave double resonance spectrometer with modulated pump power strongly depends on complete suppression of leakage signals from high pump power. Possible mechanisms of leakage signals have been investigated carefully. Adequate countermeasures have been designed to efficiently suppress leakage signals for both amplitude and frequency modulation of the pump power. A versatile microwave-microwave double resonance spectrometer is described, which offers convenient operation over large frequency ranges. In an appendix typical line shapes are given and compared to theoretical expectations.