The properties of the hydrogen-bonded dimer (CH3)3N⋅⋅⋅HCN from an investigation of its rotational spectrum

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Abstract
The ground-state rotational spectra of the three symmetric-top isotopomers (CH3)143N ⋅⋅⋅HC14N, (CH3)143 N⋅⋅⋅HC15N, and (CH3)143 N⋅⋅⋅DC15N of a hydrogen-bonded dimer formed from trimethylamine and hydrogen cyanide have been investigated by pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectroscopic constants B0, DJ, DJK, χ(14N1), and χ(14N2) have been determined from analyses of the spectra and for the isotopomer (CH3)143 N⋅⋅⋅HC14N take the values 1373.6236(2) MHz, 0.694(10) kHz, 98.52(2) kHz, −5.061(14) MHz, and −4.533(16) MHz, respectively. The spectroscopic constants have in turn been interpreted with the aid of a model of the dimer to yield the following molecular properties for the species (CH3)143 N⋅⋅⋅HC14N: r(N⋅⋅⋅C)=3.1035(6) Å, the subunit oscillation angles θav=13.4(2)°, and φav=9.1(4)° for the (CH3)3N and HCN subunits, respectively, and the hydrogen bond stretching force constant kσ=14.7(2) N m−1. The opportunity has been taken to determine a more accurate value χ0(14N)=−5.5024(25) MHz for the 14N-nuclear quadrupole coupling constant of free (CH3)143 N. The properties of the family of dimers R3N⋅⋅⋅HX, where R=CH3 or H and X=CN or CCH, are compared.