Microwave Fourier-transform spectrometer for the entire <i>K</i> band for the investigation of rotational spectra of molecules in the gas phase

Self Cite

Section: Methodsmentioning

confidence: 99%

Investigation of the Microwave Spectrum of Perchlorylfluoride by Microwave Fourier Transform Spectroscopy

Heldmann

Dreizler

1990

Self Cite

“…If inter preted within a simplified MO treatm ent, the data show that the out-off-plane p-electron density at the Nitrogen nucleus is appearently larger than the in-plane density, contrary to the prediction of a CN D O /2 calculation.Unaware of a previous study by B. Bak and coworkers [1] we have assigned and analysed the vibronic ground state rotational spectrum of Parafluoro-benzonitrile, using the high sensitivity/high resolution microwave Fourier transform spectrom eter developed by H. Dreizler and coworkers [2,3,4,5] to record the spectrum. In view of the fact that Bak et al did not resolve the l4N hyperfine struc ture of the rotational transitions, we present our results in the following note.…”

mentioning

confidence: 99%

Quadrupole Coupling in 4-Fluoro-benzonitrile. A Microwave Fourier Transform Study

Böttcher

Sutter

1986

The l4N quadrupole hfs coupling has been studied in Para-fluoro-benzonitrile using the high resolution microwave Fourier transform spectrometer constructed at Kiel University. If inter preted within a simplified MO treatm ent, the data show that the out-off-plane p-electron density at the Nitrogen nucleus is appearently larger than the in-plane density, contrary to the prediction of a CN D O /2 calculation.Unaware of a previous study by B. Bak and coworkers [1] we have assigned and analysed the vibronic ground state rotational spectrum of Parafluoro-benzonitrile, using the high sensitivity/high resolution microwave Fourier transform spectrom eter developed by H. Dreizler and coworkers [2,3,4,5] to record the spectrum. In view of the fact that Bak et al. did not resolve the l4N hyperfine struc ture of the rotational transitions, we present our results in the following note.The sample, white cristals at room temperature, was obtained from Aldrich Chemie, Steinheim (purity > 99%). The X-through K-band spectrum (8 to 25 GHz) was recorded at cell temperatures between -2 5°C and -39 °C and at sample pres sures below 1 mTorr. The sample proved stable in the brass waveguide absorption cells. (Bak and coworkers used a flow system.)In total 111 different rotational transitions, most split by the l4N quadrupole hfs interaction, were analysed in detail. In Table 1 we give a small portion of the recorded spectrum, showing the complete set of J = 4 to J = 5 transitions and some selected J = 12 to 13 transitions. The complete list is available upon request [6]. In Fig. 1 we present the 9063.5 MHz to 9064.2 MHz region of the spectrum in order to demonstrate the typical resolu tion and signal to noise ratio obtained in the present investigation. The spectrum was analysed by an iterative treat ment of the centrifugally distorted rotor (program ZFAP4 written by Typke [7]) and the hfs inter action (program HT1NQ, written by Herberich [8]) similar to the procedure described in [9]. The resultant rotational constants and 14N quadrupole coupling constants are given in Table 2. Also given for comparison are the 14N quadrupole coupling constants observed in Benzonitrile [10] and Cyanoacetylene [11], It is quite obvious, that by substitu tion to the aromatic ring, the quadrupole coupling tensor of the C = N group has lost the cylindrical symmetry usually found in small organic molecules [12], and we will try to discuss the observed asym metry in terms of p-electron densities at the N nucleus.If one analyses the observed quadrupole coupling tensor within a simplified molecular orbital theory in which the intramolecular electric field gradient at the N nucleus is assumed to be essentially deter mined by the integrals involving the atomic porbitals centered at the N nucleus, the following expression for the couplina constants is obtained [13]:( 1) (and cyclic permutations). In (1) e qn_ i . 0 Q represents the quadrupole coupling contribution of an electron in the atomic Nitrogen p-orbital (n = 2 for Nitro gen), and Paa= 2 Yj c2 nPa etc. rep...

“…We first attempted to measure the spectra with our waveguide MWFT spectrometers [13][14][15][16] decided to use our molecular beam (MB) MWFT spectrometer [17,18]. As we did not succeed to premix the SOCl 2 with argon, we soaked glass wool with the substance.…”

Section: Methodsmentioning

confidence: 99%

Nuclear Quadrupole Coupling in the Rotational Spectrum of Thionyl Chloride

Merke

Dreizler

1992