Rotational spectrum and structure of CF3H–NH3

Abstract

The rotational spectrum of CF3H–NH3 has been obtained using a pulsed nozzle Fourier transform microwave spectrometer. A symmetric top spectrum is observed that is consistent with free internal rotation of the NH3 subunit against the CF3H subunit. Rotational transitions have been measured for both the ground and first excited internal rotor state of the complex. The spectroscopic constants which have been obtained include: B0=1996.903(2) MHz, DJ =3.46(12) kHz, and eQqN =−3.186(8) MHz. From the quadrupole coupling constant of the nitrogen nucleus, eQqN, the bending amplitude of the NH3 unit is determined to be 22.57(10)°. The hydrogen bond length is 2.314(5) Å and the weak bond stretching force constant is 0.066(2) mdyn/Å. The bond length and stretching force constant for CF3H–NH3 are similar in value to those determined for HCCH–NH3 (2.33 Å and 0.070 mdyn/Å, respectively).