Emission spectra from single rovibronic quantum states in S1 benzene after Doppler-free two-photon excitation

Dispersed emission from single rovibronic quantum states in S1 benzene is measured after Doppler-free two-photon excitation under low pressure conditions (0.3 Torr). This was made possible by a long-term stabilization of the single-mode dye laser yielding a stability of better than 1 MHz/h. The emission spectra of unperturbed rotational levels in the 141 and the 14111 vibronic states reveal a great number of detailed results on Duschinsky rotation and long-range Fermi resonances in the electronic ground state. By contrast, it is seen that the emission spectra from perturbed rovibronic states are contaminated by additional bands. The analysis of these bands leads in most cases to an identification of the coupled dark background state and the responsible rotation–vibration coupling process (H42 resonances). The emission spectra clearly demonstrate that even for a density of states of 60 1/cm−1, coupling in S1 benzene is still selective and far from the statistical limit. It is further demonstrated that the dark and the light states are more efficiently mixed by short-range couplings with coupling matrix elements of some GHz than by long-range Fermi resonances. The Journal of Chemical Physics is copyrighted by The American Institute of Physics

Pathways for Intramolecular Relaxation in S1 Benzene

Sub-Doppler spectra of various one- and two-photon vibronic bands of benzene are discussed and analysed to determine the pathways of intramolecular relaxation for S1 benzene. New results are presented for the 14011011622 band of C6H6 and the 1401102 band of 13C6H6. The decay behaviour depends strongly on the excess energy and the rotational quantum numbers rather than on the vibrational character and symmetry of the excited state. At low vibrational excess energy the pathway for intramolecular relaxation is a coupling in the strong limit between pairs of states in S1 leading to shifts of lines, whereas at intermediate excess energy coupling in the weak limit to background states in S1 is present. These background states are strongly broadened due to a fast electronic non-radiative process. The intramolecular relaxation is found to be initiated by the coupling to the broadened S1 background states and energy can flow via these states to the T1 or S0 state. The rotationally selective disappearance of lines is believed to be due to an intricate interplay of the rotational dependence of the coupling matrix elements and accidental resonances, which lead to interference of possible decay channels

High Resolution Sub-Doppler Experiments on Benzene

It is shown that sub-Doppler spectroscopy enables one to resolve individual rotational states in the S^ manifold of polyatomic molecules. This i s an essential to the understanding of the primary photophysics within the molecule. Spectra of benzene are found to undergo substantial changes as the vibrational energy i s raised within S^. Due to the increased density of vibrational states, Coriolis coupling, which is already seen at low energies, can lead to effective IVR above 3000 cm""1 excess energy. This onset of IVR may be responsible for the onset of "Channel Three" in benzene and probably produces gross changes in the photophysical behavior of any polyatomic molecule

Sub-Doppler High-Resolution Spectra of C6H6

We have measured the Doppler-free rotationally resolved two-photon spectrum of two vibronic bands of C6H6, 14; 1; and 14; 1:. Compared to the 14; 1; band (E,,,, = 2492 cm-’) a drastically reduced number of sharp lines is observed in the 14; 1: band (EexCe=88 3 412 cm-’1. The K = 0 rotational lines are still seen, while K # 0 lines disappear. This can be understood in terms of Coriolis coupling between the 14l l2 state and other vibrational states within Sl and a subsequent nonradiative process. This coupling might be the explanation for the drastic onset of line broadening in C6H6 at an excess energy of 3000 cm-l, “channel three”. The line broadening is then due to a different process than that responsible for the population lifetime of S1

The problem of off duty time in long duration space missions. Volume 3 - An annotated bibliography

Annotated bibliography on studies pertaining to off duty time during long duration manned space flight

Quantifier elimination in C*-algebras

The only C*-algebras that admit elimination of quantifiers in continuous logic are $\mathbb{C}, \mathbb{C}^2$, $C($Cantor space$)$ and $M_2(\mathbb{C})$. We also prove that the theory of C*-algebras does not have model companion and show that the theory of $M_n(\mathcal {O_{n+1}})$ is not $\forall\exists$-axiomatizable for any $n\geq 2$.Comment: More improvements and bug fixes. To appear in IMR

Off-duty activity equipment and facilities for advanced spacecraft /preliminary design/

Off-duty activity equipment and facilities preliminary design for advanced spacecraf