Fourier transform microwave spectroscopy of isotopically substituted diacetylenes: rs-structure, quadrupole coupling, and anisotropic nuclear spin-spin interaction |
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Authors: | Keiji Matsumura R.D. Suenram Takehiko Tanaka |
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Affiliation: | a Seinan Gakuin University, Nishijin, Sawaraku, Fukuoka 814-8511, Japan b Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8441, USA c Kyushu University, Hakozaki, Higashiku, Fukuoka 812-8581, Japan |
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Abstract: | Monodeuterated diacetylene (HCCCCD) and its 13C-substituted species H13CCCCD, HC13CCCD, HCC13CCD, and HCCC13CD were investigated by Fourier transform microwave spectroscopy. The D nuclear quadrupole splittings were almost completely resolved. For H13CCCCD hyperfine splittings caused by the anisotropic nuclear spin-spin interaction between the H and 13C nuclei were also observed. The analysis yielded rotational constants, centrifugal distortion constants, and the constants for the nuclear quadrupole coupling and anisotropic nuclear spin-spin interaction. The substitution structure of HCCCCD was calculated as follows: rs(C-H) = 1.056054(39) Å, rs(CC) = 1.208631(4) Å, rs(C-C) = 1.374117(6) Å, rs(CC) = 1.208116(4) Å, and rs(C-D) = 1.056231(17) Å, in the order of the arrangement of the bonds. A rough estimate of the equilibrium structure is also presented. The eQq constant for the deuterium nucleus is 0.2061(4) MHz. The anisotropic 13C-H spin-spin interaction constant was experimentally determined for the first time as b = −29.2(15) kHz, which is defined as the coefficient of (3I2zI3z − I2 · I3), where I2 and I3 denote the H and 13C nuclear spins, respectively, and I2z and I3z their components along the molecular axis. The observed b constant is not accounted for by the direct magnetic dipole-dipole interaction only, suggesting a significant contribution from indirect anisotropic interaction. |
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Keywords: | Diacetylene Fourier transform microwave spectroscopy Deuteration 13C substitution rs-structure Equilibrium structure Nuclear quadrupole interaction Anisotropic nuclear spin-spin interaction Nuclear magnetic dipole-dipole interaction |
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