Else Kloster-Jensen

Emission spectra of the radical cations of diacetylene (Ã2Πu→X̃2Πg), triacetylene (Ã2Πg→X̃2Πu), and tetraacetylene (Ã2Πu→X̃2Πg,O00), and the lifetimes of some vibronic levels of the à states

Abstract The emission spectra of the radical cations of tricetylene, A 2 Π g →X 2 Π u band system, and of tetraacetylene, A 2 Π u →X 2 Π g O o o band, excited in the gaseous phase by controlled electron impact, are reported. The emission spectrum of diacetylene cation, A 2 Π u →X 2 Π g band system, with corrected band intensities is also presented. The lifetimes of the lowest vibrational level of the A 2 Π excited states have been measured as 71±3 ns, 17±2 ns and ⩽6 ns for the cations of diacetylene, triacetylene and tetraacetylene respectively. The lifetimes of the measured excited vibronic levels are shorter. Emission bands from the radical cation of cyanoacetylene and cyanogen were however not detected and these results are discussed.

Emission spectra of two C6H6+ cations in the gas phase: competition of the radiative, Ã(π−1) → X̃(π−1), and fragmentation decay of the Ã(π−1) excited state of 2,4- and 1,3-hexadiyne radical cations

Abstract The radiative relaxation of the first excited states, A(π −1 ), of two C 6 H 6 + radical cations in the gaseous phase has been detected following excitation by low energy electron impact. The A 2 E u → X 2 E g emission band system of 2,4-hexadiyne cation, and the O 0 0 band of the corresponding emission of 1,3-hexadiyne cation, which are identified by comparison with their photoelectron spectra are presented and discussed. The decay of the A(π −1 ) excited states of these C 6 H 6 ∓ ions is exceptional as the fragmentation and radiative pathways are competitive and are both detected experimentally. The lifetime of the A 2 E u state of 2,4-hexadiyne radical cation was measured to be 24 ± 2 ns, which considered together with the upper limit of 0.6 for the quantum yield of emission inferred from the cation breakdown diagram of the A 2 E u state, indicates that the radiative and non-radiative pathways deplete the A 2 E u state at approximately the same rate of 2 × 10 7 s −1 . The implications of the observations of the radiative relaxation of these two electronically excited C 6 H 6 ∓ radical cations lying above the fragment ion appearance potentials are considered with respect to the isomerization and fragmentation of C 6 H 6 ∓ isomers.

Some Aspects of Acetylene Photoelectron Spectroscopy

Recent work concerning the photoelectron spectra of unsubstituted and substituted acetylenes and polyacetylenes is reviewed. It is shown that these systems are ideal cases for the investigation of some of the principles which govern photoelectron spectra of organic compounds.

The preparation of monochloro-, monobromo- and monoiododiacetylene

Abstract Monolithium diacetylide was prepared in ether solution and reacted with molecular halogen to give the unstable monochloro- (I), monobromo- (II) and monoiodo- (III) diacetylene. Pure I, II and III were isolated (I and II by GLC) and characterized by their IR absorption spectra. Experimental evidence of the general applicability of the procedure in preparing 1-bromoalk-1-ynes is given.

The vibrational spectra of dichloro-, dibromo-, diiodo-, bromochloro- and chloroiodoacetylene

Abstract The infrared spectra of three dihaloacetylenes with equivalent halogens (dichloro-, dibromo- and diiodoacetylene) and two with different halogens (bromochloro- and chloroiodo- acetylene) were recorded in the region 4000-50 cm−1. They were studied in the vapour phase and in solution, but the less volatile diiodoacetylene was recorded in solution and as a solid. Using helium-neon laser excitation, Raman spectra of all the compounds were recorded and the depolarization ratio of the bands determined. For each of the molecules the five fundamental frequencies were assigned, and they agreed reasonably well with the frequencies derived from a preliminary force constant calculation. A progression of “hot bands” were observed at the low frequency side of the CC stretching fundamental for all the molecules.

Vibrational spectra and force field of triacetylene

Abstract The infrared and Raman spectra of triacetylene were examined in the region 4000-40 cm −1 . The infrared spectrum was recorded in the gas phase and in solution, while the Raman spectrum was obtained from a pentane solution at −20 to −30°C. The spectra were interpreted in terms of a linear structure of D ∞h -symmetry. Force constant calculations were carried out and the force constants adjusted to fit accurately the fundamental frequencies.

Infra-red spectra, vibrational assignments, and force constants of some monohalogeno diacetylenes, including force constants of some halogeno cyanoacetylenes

Abstract The infra-red spectra of the monohalogeno diacetylenes HCCCCX (X = Cl, Br and I) have been recorded in the gaseous phase and in solution in the region 4000-280 cm−1. These spectra can be interpreted in terms of a linear structure. The spectra show a striking similarity and the assignments have been supported by the band contours. Force constant calculations have been made for the monohalogeno diacetylenes as well as for the corresponding halogeno cyanoacetylenes. The force constants are adjusted to fit accurately the fundamental frequencies. Finally, the mean amplitudes of vibration and the Bastiansen—Morino shrinkage effect for these molecules are reported.

Structure and barrier to internal rotation of biphenyl derivatives in the gaseous state: Part 2. Structure of 3,3′-dibromo-, 3,5,4′ -tribronio- and 3,5,3′5′ -tetrabromobiphenyl

Abstract Gas-phase electron diffraction structures of the title compounds have been determined. The structure parameters were found to be: 3,3′-Dibromobiphenyl: r(Br) = 1.892(2), r(CC) ave = 1.398(1), r(ClCl′) = 1.504(5), r(CH)ave = 1.093(5), ∠C6C1C2 = 121.4(4), ∠C2C3Br = 119.4(4). 3,5,4′-Tribromobiphenyl: r(C3Br3) = 1.885(2), r(C4Br4′) = 1.892(2), r(C1C2) = 1.396(1), r(C2C3) = 1.399(1), r(C3C4) = 1.396(1), r(C1′C2′) = 1.394(1), r(C2′C3′) = 1.398(1), r(C3′C4′) = 1.394(1), r(C1C1′)_ = 1.511(9), r(C2H2) = 1.065(6), r(C4H4) = 1.070(6), r(C3′H3′) = 1.066(6), ∠C2C1C6 = 120.5(8), ∠C1C2C3 = 118.9(6), ∠C2′C1′C6′ = 120.4(1.0), ∠C1′C2′C3′ = 120.0(2). 3,5,3′5′ -Tetrabromobiphenyl: r(CBr) = 1.889(1), r(C1C2) = 1.395(5), r(C2C3) = 1.389(7), r(C3C4) = 1.406(9), r(C1C1′) = 1.513(9), r(CH) = 1.062(6), ∠C2C1C6= 120.2(5), ∠C1C2C3 = 119.5(2). Distances ra, are given in Angstroms and angle, ∠α, in degrees referring to the dynamic model. Both static and dynamic models have been applied in investigating the large amplitude motion about the inter-ring CC bond. All title compounds are non-planar. The dynamic model (using potential function V(o) = built1 2 V2 (1 −cos 2o) + built1 2 V4(1 − cos 4o)) gave dihedral angles of 43.8(1,3)°, 42.4(2.6)° and 43.7(0.8)°, and Fourier coefficients V2 and V4 equal to 0.8(0.9) and −5.0(1.8), −1.6(1.2) and 4.5(3.7), 1.3(0.8) and −7.0(1.5) kJ mol−1, respectively for 3,3′ -dibromo-,3,5,4,′-tribromo- and 3.5.3′,5′,-tetrabromo-biphenyl. The numbers in parentheses are one standard deviation as given by least-squares refinements using a diagonal weight matrix.

The ?2Πu→?2Πg emission and the photoelectron spectrum of dicyanodiacetylene radical cation

Gas phase emission spectrum of dicyanodiacetylene radical cation has been detected. The band system which lies in the 630–770 nm wavelength region was separated from the overlapping emission bands of the cyanogen radical by recording time resolved spectra. The He(Iα) photoelectron spectrum of dicyanodiacetylene is also presented and the inferred ionization energies, vibrational frequencies and assignments are given. From the latter data the emission spectrum is assigned as the ?2Πu→?2Πg electronic transition of dicyanodiacetylene radical cation. The frequencies of the four Σ+g vibrational fundamentals for the cationic ground state have been deduced from the emission spectrum.

Far infrared spectra and thermodynamic functions of some halogeno cyanoacetylenes and monohalogeno diacetylenes

Abstract The far infrared spectra of the halogeno cyanoacetylenes ClCCCN, BrCCCN and ICCCN were recorded in the region 350-50 cm −1 and the monohalogeno diacetylenes ClCCCCH, BrCCCCH and ICCCCH between 280 and 50 cm −1 . The vibrational assignments given earlier for these molecules are confirmed and some thermodynamic functions are calculated. A low frequency vibrational mode, previously observed in the Raman spectrum of crystalline ICCCN was verified and has been attributed to an intermolecular I ⋯ N vibration.