Microwave spectrum, dipole moment and quadrupole coupling constants of 1,2,5-selenadiazole

High-resolution infrared and theoretical study of gaseous 1,2,5-selenadiazole in the 600–1400cm−1 range

“…50% of the main 80 Se isotope, we attempted to assign these series to the C 2 H 2 N 2 78 Se isotopologue. To prove this assignment, use was made of GSCDs predicted from the ground state rotational constants of C 2 H 2 N 2 78 Se obtained in [2]. In this way we were able to improve the ground state parameters for this isotopologue, and we finally assigned rotational line series due to C 2 H 2 N 2 78 Se in all six fundamental bands studied.…”

“…Here we give a brief outline of the procedure. From a simultaneous GSCD analysis of the six bands studied and the microwave measurements [2], we obtain the three rotational constants and all five quartic centrifugal distortion constants of the ground state for C 2 H 2 N 2 80 Se, as shown in Table 3. For C 2 H 2 N 2 78 Se a similar fit of the data available yields the rotational constants and only one of the centrifugal distortion constants, D J , as seen in Table 4.…”

“…The assignment program and additional fit programs used in the present work were developed at Aarhus University. We initiated the assignment process with the well resolved and isolated m 4 band using GSCDs predicted from the ground state rotational constants of C 2 H 2 N 2 80 Se [2], and established readily the (J, K a , K c ) assignment of individual lines in the P-and R-branch clusters for K a = 0-5. During the process of assignment, the ground state constants were iteratively improved and our assignment was gradually extended to higher K a .…”

“…In the present paper we investigate six fundamental bands of 1,2,5-selenadiazole in the 600-1400 cm À1 region namely: three a-type bands m 5 (A 1 ) at 726.3 cm À1 , m 4 (A 1 ) at 1005.2 cm À1 , m 2 (A 1 ) at 1359.8 cm À1 ; two b-type bands m 12 (B 1 ) at 880.3 cm À1 , m 11 (B 1 ) at 1234.1 cm À1 ; and the c-type m 14 (B 2 ) at 833.8 cm À1 . Together with the published ground state microwave measurements from [2] this yields data for determination of precise ground state constants for the molecule. Most of the bands studied are unperturbed or only slightly affected by resonance, and upper state constants have been obtained for the bands from the Watson model.…”

“…al. [2] showed that 1,2,5-selenadiazole is a planar C 2v molecule with the a-inertial axis coinciding with the twofold rotation axis. The vibrational assignment of the fundamental bands was performed in 1968 by Benedetti and Bertini [3] from infrared and Raman spectra, and this assignment was confirmed in 1995 by El-Azhary [4] from force field calculations at MP2 level of theory.…”