The microwave spectrum of the C2H2…AgI complex assigned and analysed using PGOPHER

Abstract

Rotational spectra of four isotopologues of C2H2…AgI have been recorded between 6.5 and 18.5 GHz by chirped-pulse Fourier transform microwave spectroscopy. The complex is generated through laser ablation of a silver target in the presence of a gas sample containing low concentrations of C2H2 and CF3I in argon undergoing supersonic expansion. Rotational constants, A0,B0 and C0, centrifugal distortion constants, ΔJ and ΔJK, and nuclear quadrupole coupling constants, χaa(I) and χbb(I) − χcc(I) have been determined through spectroscopic assignment and fitting in Western’s PGOPHER program. The experimental results are reported alongside those of ab initio calculations at the CCSD(T)(F12*)/AVTZ level. The complex is shown to adopt a C2v, T-shaped geometry and structural parameters are evaluated. The r0 parameters that respectively represent the bond distance separating the two carbon atoms of C2H2, denoted as r(CC), and the CCH angle, denoted as ∠(*−C−H), are determined to be 1.2228(40) Å and 187.4(6)◦, respectively. This implies that the geometry of the C2H2 sub-unit of the complex is distorted from the geometry of the isolated C2H2 molecule. The CC bond lengthens by 0.0162(41) Å and C2H2 bends away from linearity by 7.4(6)° on formation of the complex between C2H2 and AgI where r0 parameters are used for the comparison. Trends in the force constants of bonds, and in the nuclear quadrupole coupling constant of the iodine nucleus, χaa(I), for B…AgI complexes are examined where B is varied across the series (B = Ar, H3N, H2O, H2S, C2H2, H3P and CO).