Dieter Klapstein

Lifetimes of N2O+(Ã2Σ+) and COS+(Ã2Π) in selected vibronic levels

Abstract Lifetimes of selected vibrational levels of the predissociated A 2 Σ + and A 2 Π electronic states of N 2 O + and COS + , re- spectively, have been measured. These values have been used in conjunction with previous data on fluorescence quantum yields to obtain predissociation rates for the various vibrational levels.

The emission spectrum of the 2,4-hexadiyne cation in a supersonic free jet

Abstract The A 2 E u →X 2 E g emmion band system of the vibrationally and rotationally cooled 2,4-hexadiyne cation has been obtained by electron-impact excitation of the molecule seeded into a supersonic helium free jet. The Spectrum could be recorded at high resolution, enabling vibrational frequencies to be determined with an accuracy of 0.5–1.0 cm −1 .

The [Btilde] 2 A″2 → [Xtilde] 2 E″ transition of 1,3,5-C6F3H3 + and 1,3,5-C6F3D3 + in discharge and supersonic free jet emission sources

Emission spectra of 1,3,5-C6F3H3 +(h 3 +) and 1,3,5-C6F3D3 +(d 3 +) ions were obtained by electron impact in seeded He and Ar supersonic free jets. The h 3 + (and d 3 +) spectra were recorded between 4570 (4445) A and 4820 (4810) A with a resolution R of the order of 0·5 cm-1. Gas phase discharge emission spectra of the same ions were photographed at R=0·25 cm-1 from 4450 to 4800 A and R=0·1 cm-1, between 4500 and 4700 A, and are compared to the jet cooled spectra. This comparison leads to some new or refined spectral assignments. Jet cooled and Ne matrix ion emission spectra are also compared, particularly with regard to frequencies and relative intensities of bands exhibiting the Jahn-Teller effect in the [Btilde] 2 A″2-[Xtilde] 2 E″ transition. Matrix dependent effects on Jahn-Teller levels and interaction parameters are observed and discussed. Rotational contour analysis of peak structures in the 00/0 and 61,1/2/0,0 emission bands in the discharge and jet spectra of the h 3 + ion indicates that ΔB ⋍ -...

Ã2Σ+ → X̃+Π Emission spectra of the phosphaethyne cations, HCP+ and DCP+

Abstract The electron impact excited A 2 Σ + → X + Π emission spectra of HCP + and DCP + have been observed. The spin-orbit split 0-0 band has maxima at 593.7 and 599.0 nm for HCP + and 593.6 and 598.8 nm for DCP + . Short progressions in the V 3 (CP) vibration are observed. a 0 , v 3 and the upper-state lifetime are determined.

2Σ+ → 2Πi emission spectra of the phosphaethyne cations HCP+ and DCP+

Abstract Electron impact excited A 2Σ+ → X 2Πi emission spectra of HCP+ and DCP+ have been observed. The spectra consist of short progressions in ν″3. The 0 000 → 0 010 bands have been studied under high resolution and rotational analyses carried out. Some of the more important derived constants are (in cm−1) HCP+; ν″3 = 1150(10), A″0 = -146.97(3), B″0 = 0.6224(16), B′0 = 0.6690(17); DCP+; ν″3 = 1110(10), A″0 = -146.71(1), B″0 = 0.5284(2), B′0 = 0.5682(2).

Emission spectra of rotationally cooled dihaloacetylene cations in the gas phase: Ã2ΠΩ,g → X̃2ΠΩ,u band systems

Abstract The A 2 Π Ω,g → X 2 Π Ω,u , Ω = 3/2, 1/2 emission spectra of rotationally colled dichloro-, dibromo- and diiodo-acetylene c???tions in the gas phase have been obtained. This is achieved by electron-impact ionisation of the molecular species seeded in a helium supersonic free jet. The effect of the rotational cooling is that the vibronic bands are sharp and the isotope b???nds are clearly discernible, allowing the spectra to be vibrationally analysed. The vibrational frequencies of most of the fundamentals could be determined to within ±1 cm −1 for both the Ω = 3/2 and 1/2 components of the ground and first excited electronic states.

Vibrational spectra of acetyl isocyanate and mono-, di- and trichloroacetyl isocyanates

Abstract The gas-phase infrared and liquid-phase Raman spectra of R CO NCO, where R = CH3, CH2Cl, CHCl2 and CCl3, have been recorded. For each molecule an assignment of the observed bands has been proposed in terms of the two planar conformers derived from rotation about the C N bond. The observations indicate that the cisoid conformation is the preferred one in the gas phase while substantial amounts of both cisoid and transoid conformers are present in the liquid.

à 2Σ+ → [Xtilde] 2Π i emission spectra of the thioborine cations HBS+ and DBS+

The emission spectra of the A 2Σ+ → [Xtilde] 2Π i transitions of HBS+ and DBS+ have been obtained by electron impact excitation. A vibronic analysis of the band systems has been made and the vibrational frequencies of the three modes in the [Xtilde] 2Π i state, and two in the A 2Σ+ state have been obtained for various isotopic derivatives. Renner and Fermi resonance effects of the bands involving the excitation of the ν2/″ mode have been considered and the parameters characterizing these interactions evaluated.

Emission spectra of supersonically cooled chloroacetylene cations

Abstract The Ā2ΠΩ → X2ΠΩ, Ω = 3 2 , 1 2 emission spectra of rotationally cooled chloro- and deuterochloro-acetylene cations have been obtained by electron-impact ionisation of a seeded helium supersonic free jet. The resultant spectral improvements lead to the identification of the spin-orbit components and isotope splittings and to a vibrational assignment of the prominent bands. The vibrational frequencies could be determined to within ±1 cm−1 for many of the fundamentals for the cations in the X2ΠΩ and Ā2ΠΩ electronic states.

Vibrational spectra and conformational behaviour of carbonyl isothiocyanates XCONCS, XF, Cl, Br, MeO, EtO, and acetyl isothiocyanate CH3CONCS

Abstract Vibrational data for five carbonyl isothiocyanates XCONCS, with XF, Cl, Br, MeO and EtO, and for acetyl isothiocyanate CH 3 CONCS are reported. Detailed assignments for the infrared and Raman data of the -F, -Cl and -CH 3 species are given. The vapour phase IR spectrum of acetyl isothiocyanate suggests the presence of the cisoid conformer only but the spectra of all the carbonyl isothiocyanates show features which are interpreted in terms of both cisoid and transoid conformers being present. Temperature dependent IR data show that for X=Cl and Br the transoid conformation is more stable while for X=F, MeO and EtO the cisoid form is preferred. The conformeric stabilities and vibrational data are compared with recent results for the corresponding isocyanato species.