High resolution molecular beam study of the origin band of the B̃ 2Σ+–X̃ 2Σ+ system of yttrium imide

Abstract

The (0,0,0)–(0,0,0) band of the B̃ 2Σ+–X̃ 2Σ+ system of three isotopomers of yttrium imide (Y14NH, Y15NH, and Y14ND) has been studied by laser-induced fluorescence in a molecular beam apparatus. Rotational, fine, and nuclear magnetic hyperfine structures have been resolved and analyzed. The B̃ 2Σ+(0,0,0) state of Y14NH, Y14ND, and Y15NH is severely perturbed below J=30.5 by eight, three, and two vibronic states, respectively. Although, the nature of these perturbing states can only be speculated upon, their symmetries are either Σ2 or Π2, and this has made it possible to deperturb the B̃ 2Σ+ state successfully. The spectra can be reproduced within 140 MHz (0.0047 cm−1). The analyses confirm that the molecule is linear in both states with the nuclear arrangement Y–N–H. The bond lengths in the ground X̃ 2Σ+ state and the B̃ 2Σ+ state have been derived to be rY–N=1.877 57(13) Å, rN–H=1.0067(10) Å, and rY–N=1.8839(43) Å, rN–H=1.242(30) Å, respectively. The results are compared with the values of ab initio calculations on YNH and YN, and the experimental data on YN and YO. The atomic character of the unpaired electron in the ground state is 58% Y + 5s and 42% Y + 5p. The electron configurations for the ground X̃ 2Σ+ state and the B̃ 2Σ+ state are discussed and compared with ab initio calculations whenever possible.