Spectroscopic investigations of hydrogen bonding interactions in the gas phase. VIII. Microwave rotational spectrum of the heterodimer H—C≡C—C≡N ∙ ∙ ∙ HF

The hydrogen bonded dimer formed between cyanoacetylene and hydrogen fluoride has been identified through its infrared and microwave spectra. Two microwave techniques, continuous wave and pulsed-nozzle Fourier-transform spectroscopy, have been combined to identify unambiguously the vibrational ground state transitions and to assign vibrational satellites. In making the assignments, much use has been made of computer simu­lation of spectra, which is described in an Appendix. Analysis of the microwave spectra led to the following spectroscopic constants and molecular parameters. HC 3 N ∙ ∙ ∙HF HC 3 N∙ ∙ ∙DF B 0 /MHz 1220.68431 (9) 1204.9051 (2) D J /kHz 0.306 (2) 0.296 (3) α β /MHz ─7.20 (2) — γ β /MHz 0.094 (3) — γ 11 /MHz ─0.030 (2) — α σ /MHz ─13.7 (2) — q β /MHz 3.12 (2) — r 0 (N ∙ ∙ ∙ F)/nm 0.2788 0.2785 X /MHz ─ 3.876 ─ 3.854 v β /cm -1 30 — v σ /cm -1 139 — k σ /(N m -1 ) 16.3 — k s /(N m -1 ) 770 — Finally, the variation of ∆ v̄ as a function of r 0 (N ∙ ∙ ∙ F) has been examined for a series of dimers RCN ∙ ∙ ∙ HF.