Pulsed Doppler-free two-photon spectroscopy of polyatomic molecules

Doppler-free two-photon electronic spectra of a large polyatomic molecule are recorded for the first time with pulsed laser radiation of near Fourier-transform limited bandwidth (Δv～100 MHz). The resolution obtained is sufficient to resolve individual rotational lines. Due to the high density of these rotational transitions a strong Doppler-broadened background is observed, which is, however, subtantially reduced by suitable choice of photon polarizations. Different vibronic bands of benzene (C₆H₆) are investigated and very accurate rotational constants are found.     

Anharmonic effect on unimolecular reactions with application to the photodissociation of ethylene

The importance of anharmonic effect on dissociation of molecular systems, especially clusters, has been noted. In this paper, we shall present a theoretical approach that can carry out the first principle calculations of anharmonic canonical and microcanonical rate constants of unimolecular reactions within the framework of transition state theory. In the canonical case, it is essential to calculate the partition function of anharmonic oscillators; for convenience, the Morse oscillator potential will be used for demonstration in this paper. In the microcanical case, which involves the calculation of the total number of states for the activated complex and the density of states for the reactant, we make use of the fact that both the total number of states and the density of states can be expressed in the inverse Laplace transformation of the partition functions and that the inverse Laplace transformation can in turn be carried out by using the saddle-point method. We shall also show that using the theoretical approach presented in this paper the total number of states and density of states can be determined from thermodynamic properties and the difference between the method used in this paper and the thermodynamic model used by Krems and Nordholm will be given. To demonstrate the application of our theoretical approach, we chose the photodissociation of ethylene at 157 and 193 nm as an example.     

High-resolution mass-selective UV spectroscopy of pseudoephedrine: evidence for conformer-specific fragmentation

Using resonance-enhanced two-photon ionization spectroscopy with mass resolution of jet-cooled molecules, a low-resolution S(1) ← S(0) vibronic spectrum of pseudoephedrine was recorded at the mass channels of three distinct fragments with m/z = 58, 71, and 85. Two of the fragments, with m/z = 71 and 85, are observed for the first time for this molecule. The vibronic spectra recorded at different mass channels feature different patterns, implying that they originate from different conformers in the cold molecular beam, following conformer-specific fragmentation pathways. Highly resolved spectra of all prominent vibronic features were measured, and from their analysis based on genetic algorithms, the molecular parameters of the conformers giving rise to the respective bands have been determined. Comparing the experimental results with those obtained from high-level ab initio quantum chemistry calculations, the observed prominent vibronic bands have been assigned to originate from four distinct conformers. The conformers are separated into two groups that have different fragmentation pathways determined by the different intramolecular interactions.     

Die Bestimmung der Metallsulfide durch Erhitzen im Schwefelwasserstofstrom

Ohne Zusammenfassung     

Fast observation of primary triplets in naphthalene vapor with tandem laser pulse absorption

A sharply tuned pulsed laser absorption experiment is described involving two dye lasers synchronized in tandem (TLPA) which enables one to produce molecules in defined excited states and then follow the immediate production of subsequent molecular species. Measurements of transient TT absorption were carried out in naphthalene at pressures down to 20 mtorr with a precision of 0.2%. The results demonstrate the feasibility of TLPA and here specifically that triplets are formed in naphthalene as a prompt process, and that collisions do not aid the formation of these primary product species.     

On the groups of c-projective transformations of complete Kähler manifolds

We show that for any complete connected Kähler manifold, the index of the group of complex affine transformations in the group of c-projective transformations is at most two unless the Kähler manifold is isometric to complex projective space equipped with a positive constant multiple of the Fubini–Study metric. This establishes a stronger version of the recently proved Yano–Obata conjecture for complete Kähler manifolds.     

Evidence for second-phonon nuclear wobbling

The nucleus 163Lu has been populated through the reaction 139La(29Si,5n) with a beam energy of 157 MeV. Three triaxial, strongly deformed (TSD) bands have been observed with very similar rotational properties. The first excited TSD band has earlier been assigned as a one-phonon wobbling excitation built on the lowest-lying (yrast) TSD band. The large B(E2)(out)/B(E2)(in) value obtainable for one of four observed transitions between the second and first excited TSD bands is in good agreement with particle-rotor calculations for a two-phonon wobbling excitation.     

Gamma-ray feeding and decay of superdeformed states

We report on four recent results concerning the population and the decay of superdeformed states, namely the structure of excited superdeformed states in ¹⁹⁴Hg, the search for fine structure of the last superdeformed transitions in ¹⁹⁴Pb, the primary decay-out strength analysis in ¹⁹⁴Hg and, as a consequence of this, the possibility of using the decay-out as a tool to study order-to-chaos properties of normally deformed states.Received: 3 December 2002, Published online: 17 February 2004PACS: 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 24.60.-k Statistical theory and fluctuations - 24.60.Lz Chaos in nuclear systems - 27.80. + w F. Hannachi: Present address: CENBG/IN2P3, Gradignan, France.H. Amro: Present address: WNSL, Yale, USA.K. Hauschild: Present address: CSNSM/IN2P3, Orsay, France.T. Kröll: Present address: TU, Munich, Germany.M. Rejmund: Present address: GANIL, Caen, France.     

The spectrum of collision free triplets and its temporal evolution

A tandem laser experiment now enables one to follow the time history of the radiationless formation of triplets from inception to the final relaxed state known from flash photolysis. The TT absorption spectrum is measured shortly after excitation of the singlet and then at different times up to full relaxation at 14 μs. This spectrum is totally different from the well known flash photolysis spectrum, both in spread and its structure. The spectrum reveals both a relaxation process to thermalized triplets, as well as direct evidence for overall loss of triplets by a further radiationless process. Quantitative data can here be presented for these processes.     

High resolution lifetime measurements of isolated vibronic levels in naphthalene C10H8

A frequency-doubled, continuous tunable dye laser has been employed with a bandwidth of 0.5 cm^?1 in the UV to yield high resolution dynamic information about vibronic excited states of naphthalene in the collisionless region. The results show strong variations of lifetimes in the various sequence modes identified in high resolution absorption spectra. The evidence points to a strong contribution from both Franck—Condon factors as well as symmetry considerations.