Rotational spectra and nitrogen nuclear quadrupole coupling for the cyanoacetylene dimer: H[sbnd]C[tbnd]C[sbnd]C[tbnd]N⋯H[sbnd]C[tbnd]C[sbnd]C[tbnd

Abstract

The rotational spectra of cyanoacetylene dimer, HCCCN⋯HCCCN, were recorded using Balle–Flygare type Fourier transform microwave (FTMW) spectrometers. The low J transitions were measured down to 1.3GHz at very high resolution, FWHM∼1kHz. The spectral hyperfine structure due to the 14N nuclear quadrupole coupling interactions is well-resolved below 4GHz using a low frequency spectrometer at the University of Arizona. The experimental spectroscopic constants were fitted as: B0=339.2923310(79)MHz, DJ=32.152(82)Hz, H=−0.00147(20)Hz, eqQ(14N1)=−3.9902(14)MHz, and eqQ(14N2)=−4.1712(13)MHz. The vibrationally averaged dimer configuration is HCCCN⋯HCCCN. Using a simple linear model, the vibrational ground state and the equilibrium hydrogen bond lengths are determined to be: r0(N⋯H)=2.2489(3)Å and re(N⋯H)=2.2315Å. The equilibrium center-of-mass distance between the two HCCCN subunits is rcom=7.0366Å. Using the rigid precession model, the vibrational ground state center-of-mass distance and the pivot angles which HCCCN subunits make with the a-axis of HCCCN⋯HCCCN are rc.m.=7.0603Å, θ1=13.0°, and θ2=8.7°, respectively. The calculated hydrogen bond energy of HCCCN⋯HCCCN is 1466cm−1 using the MP2/aug-cc-PVTZ method in present work.