THE EFFECT OF ACIDS ON THE INFRARED SPECTRA OF SCHIFF BASES—II. IMINES CONTAINING THE C=C-C=N AND C=C-C=C-C=N UNITS

Abstract— The Fourier-transform infrared spectra of chloroform-d solutions of conjugated imines CH₃CH=CHCH=NCH(CH₃)₂ and CH₃CH₂CH=CHCH=CHCH=NCH(CH₃)₂ and the related protonated species with HCl, HBr, HI, trichloro, dichloro, monobromo and monochloroacetic acids or propionic acid are presented. The effects of conjugation and protonation are examined. The results show that conjugation slightly increases the basicity of the Schiff bases. HCl, HBr and HI protonate the Schiff bases completely. The carboxylic acids protonate partially depending on their p K _a, values. When the Schiff base contains two (or more) C=C bonds conjugated with C=N, the main C=C stretching band undergoes a strong intensification showing that sizeable dipole moment variations occur along the conjugated chain.     

Investigation of Rare Pion Decays with the PIBETA Spectrometer

Experimental results on pion decays obtained with the PIBETA spectrometer at the Paul Scherrer Institute (PSI) are reviewed. For pion beta decay π⁺ → π⁰е⁺ν (πβ), a precision measurement of relative probability yields Г(πβ) = [1.036 ± 0.004(stat) ± 0.004(syst) ± 0.003(π⁺→е⁺ν)] × 10^–8, which implies V_ud = 0.9728(30) for the corresponding element of the Cabibbo–Kobayashi–Maskawa mixing matrix. Using a sample of 65 × 10³ events, relative probability of the π⁺→е⁺νγ radiative pion decay (RPD) in the kinematic region of E_γ > 10 MeV and θ_eγ > 40° is measured as B^exp = 73.86(54) × 10^–8. A statistical analysis of measured E_e+ and E_γ distributions for this decay yield the values F_V = 0.0258(17) and F_A = 0.0117(17) for the pion weak formfactors. Assuming that F_V linearly depends on the е⁺ν invariant mass q² as F_V(q²) = F_V(0)(1 + aq²), the slope parameter is extracted as а = 0.10(6). The pion polarizability and neutral-pion lifetime are estimated as α_E = 2.78(10) × 10^–4 fm³ and τ(π⁰) = (8.5 ± 1.1) × 10^–17 s, respectively. The data for decays π⁺→ е⁺ ν and \({\mu ^ + } \to {e^ + }v\bar v\gamma \) have been collected and are being processed. The follow-up PEN experiment aims at reducing the uncertainty on the π⁺ → е⁺ ν relative probability by almost an order of magnitude (to 5 × 10^–4).