Rotational spectroscopy and molecular structure of 15N2-14N2O

The rotational spectrum of N-15(2) - (N2O)-N-14 has been recorded in the 7- 19 GHz region with a pulsed molecular beam, Fourier transform microwave spectrometer. An internal motion of the N-15(2) subunit has been observed and the nuclear quadrupole hyperfine structure in each internal motion state has been analyzed using the Watson S-reduced Hamiltonian with the inclusion of nuclear quadrupole coupling interactions. The spectroscopic constants of the ground internal motion state are not well determined since only 4 transitions have been observed, but they are similar to those of the excited internal motion state that are determined from the analysis of 14 a- and b- type transitions. The rotational and centrifugal distortion constants (in MHz) for the excited internal motion state are A = 12791.307 0( 2), B = 2014.982 4(1), C = 1728.950 45 (7), D-J = 1.052 5( 2) x 10(-2), D-JK = 3.933 7(3) x 10(-1), d(1) = -1.822(3) x 10(-3), d(2) = -1.118(6) x 10(-3). The nuclear quadrupole coupling constants (in MHz) in the excited internal motion state for the terminal N-14 nucleus in N2O are chi(aa) - 0.3465(4), chi(bb) = -0.7445(5), and chi(cc) = 0.3980(5), while those for the central N-14 nucleus are chi(aa) = 0.1023 (9), chi(bb) = -0.2528(8), and chi(cc) = 0.1505(8). These spectroscopic constants are consistent with a T- shaped structure, with N-15(2) forming the leg of the T. The intermolecular distance is 3.691 Angstrom. The N-15(2) axis and the (N2O)-N-14 axis make an angle of 13 degrees and 81 degrees with the intermolecular axis, respectively. The nuclear quadrupole coupling constants show electric field gradient perturbation in the N2O subunit, with the field gradient at the central nitrogen affected to a greater extent than that at the terminal nitrogen. This perturbation is likely due to electron charge redistribution in N2O upon complexation with N-2. (C) 1999 American Institute of Physics. [S0021-9606(99)01508-1].