The structure of ScC2 (X<mml:mo></mml:mover>2A1): A combined Fourier transform microwave/millimeter-wave spectroscopic and computational study

Pure rotational spectra of (ScC2)-C-13 (X</mml:mover>(2)A(1)) and (ScCC)-C-12-C-13 (<mml:mover accent="true">X<mml:mo></mml:mover>(2)A ') have been measured using Fourier transform microwave/millimeter-wave methods. These molecules were synthesized in a DC discharge from the reaction of scandium vapor, produced via laser ablation, with (CH4)-C-13 or (CH4)-C-13/(CH4)-C-12, diluted in argon. The N-Ka,N-Kc = 1(0,1) -> 0(0,0,) 2(0,2) -> 1(0,1,) 3(0,3) -> 2(0,2), and 4(0,4) -> 3(0,3) transitions in the frequency range of 14 GHz-61 GHz were observed for both species, each exhibiting hyperfine splittings due to the nuclear spins of C-13 (I = 1/2) and/or Sc (I = 7/2). These data have been analyzed with an asymmetric top Hamiltonian, and rotational, spin-rotation, and hyperfine parameters have been determined for (ScC2)-C-13 and (ScCC)-C-12-C-13. In addition, a quartic force field was calculated for ScC2 and its isotopologues using a highly accurate coupled cluster-based composite method, incorporating complete basis set extrapolation, scalar relativistic corrections, outer core and inner core electron correlation, and higher-order valence correlation effects. The agreement between experimental and computed rotational constants, including the effective constant (B + C), is similar to 0.5% for all three isotopologues. This remarkable agreement suggests promise in predicting rotational spectra of new transition metal-carbon bearing molecules. In combination with previous work on (ScC2)-C-12, an accurate structure for ScC2 has been established using combined experimental (B, C) and theoretical (A) rotational constants. The radical is cyclic (or T-shaped) with r((Sc-C)) = 2.048(2) angstrom, r((C-C)) = 1.272(2) angstrom, and angle ((C-Sc-C)) = 36.2(1)degrees. The experimental and theoretical results also suggest that ScC2 contains a C-2(-) moiety and is largely ionic.