Chlorine nuclear quadrupole hyperfine structure has been resolved and analyzed in the spectrum of three isotopic species, CH3C'5N.-H35CI, CH3C'5N-.H37C1, and CH3C15N.-D3SCI, of the methyl cyanide-hydrogen chloride hydrogen-bonded dimer. The determined spectroscopic constants are Bo = 1 100.72675 (8) MHz, D, = 0.554 (1) kHz, D,, = 64.05 (5) kHz, and eqQ = -52.45 (2) MHz for CH3C'5N-.H3SCI. These spectroscopic constants have been interpreted to give r(N..-CI) and k,, the values of which are 3.301 (4) A and 10.68 (2) N m-l, respectively, for the species CH3CISN-.H35CI. The corresponding quantities are also presented for the species CH3C'5N-.H37C1 and CH3C15N-.D35CI.
Experimental SectionThe experimental arrangement and procedures for the observation of OH adduct radicals were essentially the same as those described in the preceding paper.3 All materials were obtained from commercial sources and used without further purification. Sample solutions containing 3-10 mM substrates were saturated with nitrous oxide so that hydrated electron was converted effectively to hydroxyl radical and deoxygenation o c c~r r e d .~ To provide a basicity scale above the pH scale, our H-scale2 was used for concentrated aqueous potassium hydroxide (KOH) solutions.
Measurements of absolute intensities of rotational transitions have been used to determine the zero-point and equilibrium dissociation energies D0 and De of the hydrogen-bonded dimers CH3CN⋅⋅⋅HF and HCCCN⋅⋅⋅HF. For CH3CN⋅⋅⋅HF reported values are D0=26.1(0.6) kJ mol−1 and De=29.0(0.9) kJ mol−1 while for HCCCN⋅⋅⋅HF the corresponding values are 20.4(0.7) and 23.4(0.9) kJ mol−1, respectively. The De values are used in conjunction with De=26.1(1.6) kJ mol−1 previously obtained for HCN⋅⋅⋅HF to investigate the suitability of the Morse and Lennard-Jones functions for describing the hydrogen-bond radial potential energy.
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.
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