Vepric - Vjera roda moga

The close similarity in patterns of bands in the microwave spectra of the isomeric 1,2,3- and 1,2,4-triazines has enabled assignment for the 1,2,3-isomer. Pure rotational transitions with J up to 65 were identified and fitted to a Watson-type Hamiltonian: A = 6334.157(14)., B = 6271.289(14), C = 3151.230(14). A and B thus show near degeneracy. Coupled cluster calculations which include both singles, doubles and selected triple excitations (CCSD(T)), give very close agreement with the spectral data. The theoretical structure which includes estimates of the 14N quadrupole coupling, not determined in the spectrum, is described.PostprintPeer reviewe

MILLIMETER AND SUBMILLIMETER WAVE SPECTROSCOPIC INVESTIGATIONS INTO THE ROTATION-TUNNELING SPECTRUM OF gGg' ETHYLENE GLYCOL (HOCH2CH2OH)(HOCH_{2}CH_{2}OH)

$^{a}$D. Christen and H. S. P. M\""{u}ller, Phys. Chem. Chem. Phys. 5, (2003) 3600-3605Author Institution: I. Physikalisches Institut, Universit\""{a}t zu K\""{o}ln; Institut f\""{u}r Physikalische und Theoretische Chemie, Universit\""{a}t T\""{u}bingenGaseous ethylene glycol (1,2-ethanediol) consist of two conformers, aGg' and gGg', with the latter being ${\sim} 2.5 kJ mol^{-1}$ or ${\sim} 200 cm^{-1}$ higher in energy than the former. Both conformers exhibit intermolecular hydrogen bonding between the H atom of one OH group and the O atom of the other. Large amplitude tunneling occurs between two equivalent minima described by exchange of the roles of the H atoms of the OH groups. The two tunneling substates are separated by 6958 and 1367 MHz for aGg' and gGg' glycol, respectively, with considerable Coriolis interaction between the two substates. $Recently,^{a}$ we have reported investigations into the rotation-tunneling spectrum of the aGg' conformer in selected regions between 54 and 370 GHz. The spectrum could be reproduced within experimental uncertainties employing a comparatively small set of spectroscopic parameters. The present contribution deals with the rotation-tunneling spectrum of gGg' glycol recorded in selected regions between 77 and 579 GHz. While the quantum number range, $J \leq 55$ and $K_{a} \leq 19$, is similar to that of the aGg' study, a much larger number of transitions has been recorded because of persistent difficulties in reproducing the complete data set within experimental uncertainties. Starting to refit the transition frequencies involving low quantum numbers, it was possible to extend the line list in a consistent way to about 2/3 of the ${\sim} 1500$ transitions, i.e. to quantum numbers having $J \leq 40$ and $K_{a} \leq 4$ or $J \leq 22$ and $K_{a} \leq 17$ which could be reproduced within experimental uncertainties. Difficulties in fitting transitions with high J or $K_{a}$ may be due to extensive Coriolis interaction between the two tunneling substates combined with unavoidable correlation effects or possibly to a Coriolis interaction of the ground vibrational state of gGg' glycol with the first excited torsional state of aGg' glycol

THE MICROWAVE SPECTRUM OF 1,2,4-TRIAZINE AND THE ROTATIONAL CONSTANT OBTAINED FROM A SIMULTANEOUS ANALYSIS OF MICROWAVE GROUND STATE AND HIGH RESOLUTION IR-TRANSITIONS.

$^{a}$ Palmer, Maier, Hegelund, and Newnham, J. Mol. Spectrossc. 192, 331, (1998)and Bach, Hegelund, Beukes, Nicolaisen, and Palmer, J. Mol, Spectrose. 198, (1999)Author Institution: Institute of Physical and Theoretical Chemistry, University of T\""ubingen; Department of Chemistry, University of Edinburgh; Department of Chemistry, Aarhus UniversityThe microwave spectrum of 1,2.4-triazine has been recorded in the Ku- and Ka-bands using a conventional stark spectrometer. The low -J lines appeared close to the frequencies predicted for the ground state from the high resolution $FTIR-studies^{a}$, but to secure a correct assignment of higher J Q-branch transitions a microwave microwave double resonance experiment was done for a few of transitions sharing a common level. 145 transitions were recorded with $J_{max}=42$, $K_{a,max} =33$, and $K_{e,max} =11$. A simultaneous fit to MW pure rotational transitions and to the rotational structure of selected IR-bands led to a determination of rotational and all 5 quartic centrifugal distortion constants

THE g'Ga CONFORMER OF ETHYLENE GLYCOL: A TEST CASE FOR TUNNELING-ROTATION APPROACHES DEVELOPED FOR NON-RIGID MOLECULES

$^{a}$ Christen, Coudert, Suenram, and Lovas, J. Mol. Spectrosc. $172, 57 (1995). ^{b}$ Christen, Coudert, Larsson, and Cremer, J. Mol. Spectrosc. 205, 185 $(2001). ^{c}$ Pickett, J. Chem. Phys. 56, 1715 (1972).Author Institution: Institut f\""{u}r Physikalische und Theoretische Chemie, Universit\""{a}t T\""{u}bingen, Auf der Morgen-stelle 8; I. Physikalisches Institut, Universit\'at zu K\""oln; Laboratoire de Photophysique Mol\'eculaire, C.N.R.S., B\^at. 350, Universit\'e Paris-SudEthylene glycol $(CH_{2}OH)_{2}$ is a molecule of great interest because it displays intramolecular hydrogen bonding as well as an interconversion large amplitude motion which allows each OH groups to be put in turn into the hydrogen bond. This molecule also occurs in several conformers and at the present time only the two lowest lying forms have been spectro-scopically characterized, namely, when listed with increasing energy, the $g^{\prime}Ga^{a}$ and the $g^{\prime}Gg^{b}$ conformers. As shown by the previous $investigation,^{a}$ in the $g^{\prime}Ga$ conformer, the large amplitude motion leads to a large tunneling splitting of about 6.9 GHz which is Coriolis coupled to the overal rotation of the molecule. The new measurements of the millimeterwave spectrum carried out in K\""{o}ln confirm these results. However, they involve transitions characterized by much higher J and $K_{a}$-values than those initially measured and the theoretical approach developed $previously^{a}$ did not allow us at first to account correctly for the observed frequencies. The new data were first analyzed using an RAS fit program based on Pickett's $formalism^{c}$ and afterwards using a modified version of the IAM-like approach initially $developed.^{a}$ Although both theoretical approaches are designed to account for the Coriolis coupling between the large amplitude motion and the overall rotation of the molecule, they involve very different coupling terms. In the paper, the results of the two analysis will be presented. The differences and the analogies between the two theoretical approaches will be discussed and it will be stressed, using the results of both analyses, that there exists a transformation which allows us to obtain the spectroscopic parameters of the RAS $fit^{c}$ from those obtained in the IAM-like $formalism,^{a}$ and vice versa