Fourier transform measurement of two-photon excitation spectra: applications to microscopy and optimal control

We report a novel Fourier transform method for measuring two-photon excitation spectra. We demonstrate this method using simple dye molecules and discuss its applications in two-photon fluorescence microscopy and optimal control. This method facilitates an intuitive interpretation of recent control experiments in terms of tuning the nonlinear spectrum of the exciting laser source.     

Evaluation of Expansion Coefficients from Optimal Fitting Parameters for the Analysis of Spectra of Diatomic Molecules and an Application to LiH

To evaluate individual expansion coefficients composing fitting parameters of the Born-Oppenheimer corrections to Dunham's coefficients Y(ij) that have been given analytically with the Delta(B) and Delta(omega) formalism, we examined the consistency of analytic expressions for those corrections with Watson's assertion of the experimental inseparability of nonadiabatic corrections Q(a, b)(r) for a molecule AB. Derived analytic expressions in terms of optimal fitting parameters for the corrections are essential to evaluate individual expansion coefficients. These expressions also reveal redundancies between empirical correction parameters Delta(ij). A method of evaluating nonadiabatic vibrational corrections Q(a, b)(r) and adiabatic corrections S(a, b)(r) separately consistent with Watson's assertion of inseparability is presented and is applied to an analysis of spectral data of LiH. Functions Q(a, b) and S(a, b) for LiH are thus successfully evaluated; S(H, Li)(r) values agree well with those predicted simply by wobble-stretch theory. Experimental values for optimal fitting parameters r(H)(1q) and r(H)(2q) are nearly equal to those of r(Li)(1q) and r(Li)(2q), respectively, in agreement with a theoretical relation r(a)(iq)=r(b)(iq). Copyright 2001 Academic Press.     

Baryon rapidity loss in relativistic Au + Au collisions

An excitation function of proton rapidity distributions for different centralities is reported from AGS Experiment E917 for Au+Au collisions at 6, 8, and 10.8 GeV/nucleon. The rapidity distributions from peripheral collisions have a valley at midrapidity which smoothly change to distributions that display a broad peak at midrapidity for central collisions. The mean rapidity loss increases with increasing beam energy, whereas the fraction of protons consistent with isotropic emission from a stationary source at midrapidity decreases with increasing beam energy. The data suggest that the stopping is substantially less than complete at these energies.     

Self-sustaining nonlinear dynamo process in Keplerian shear flows

A three-dimensional nonlinear dynamo process is identified in rotating plane Couette flow in the Keplerian regime. It is analogous to the hydrodynamic self-sustaining process in nonrotating shear flows and relies on the magnetorotational instability of a toroidal magnetic field. Steady nonlinear solutions are computed numerically for a wide range of magnetic Reynolds numbers but are restricted to low Reynolds numbers. This process may be important to explain the sustenance of coherent fields and turbulent motions in Keplerian accretion disks, where all its basic ingredients are present.     

Calculation of the rotation-vibration spectrum of NH+

Ab initio molecular orbital calculations have been used to compute potential energy and dipole moment functions for the X²II and a⁴Σ^? states of NH⁺. These functions have been used to compute rotational-vibrational energy levels, including the interaction between the two states. Transition moments have been calculated for transitions between these levels, using either the results of numerical diagonalization of the Hamiltonian, or more approximately by fitting analytic functions. Good agreement with experimental data is found, and our results have also been used to interpret previously unassigned spectral lines.     

Theoretical Herman-Wallis coefficients for C70 and D70 and the dipole-moment function of HCl

Theoretical expressions for the Herman-Wallis coefficients C⁷₀ and D⁷₀ and a correction term of order 2B_e/ω_e times the leading term for C⁶₀ have been derived in terms of the Dunham potential-energy parameters and series dipole-moment expansion coefficients by the method of computer algebra. After reviewing previous work on the extraction of the dipole-moment function for HCl from experimental data, the present results are applied to a determination of the series representation up to seventh order in the reduced displacement from the equilibrium internuclear separation. Coefficients for an alternate representation in terms of a Padé approximant are also obtained; this model dipole-moment function should enable one to estimate more accurately the higher overtone and highly excited hot-band intensities since it circumvents the divergence difficulties of the series expansion and has the correct asymptotic behavior at both small and large internuclear separations.     

Fragmentation of gold projectiles: From evaporation to total disassembly

We have studied the fragmentation of Au projectiles interacting with targets of C, Al and Cu at an incident energy ofE/A=600 MeV. The employed inverse kinematics allowed a nearly complete detection of projectile fragments with chargeZ≧2. The recorded fragmentation events were sorted according to three observables, the multiplicityM _lp of light charged particles, the largest atomic numberZ _max within an event, and a new observable,Z _bound, representing the sum of the atomic numbersZ of all fragments withZ≧2. Using these observables, the impact parameter dependence of the fragmentation process was investigated. For all three targets, a maximum mean multiplicity of 3 to 4 intermediate mass fragments (IMFs) is observed. The corresponding impact parameters range from central collisions for theC target to increasingly peripheral collisions for the heavier targets. It is found that the correlation between the IMF multiplicity andZ _bound, extending from evaporation type processes (largeZ _bound) to the total disassembly of the projectile (smallZ _bound), is independent of the target nucleus. This universal behaviour may suggest an — at least partial — equilibration of the projectile fragment prior to its decay.     

Dunham potential energy coefficients of the hydrogen halides and carbon monoxide

The Dunham potential energy coefficients a_i, 0 ≤ i ≤ 6 (except 4 for HI) have been derived from spectroscopic data of hydrogen halides HF, HCl, HBr, and HI, and carbon monoxide in their ground electronic states. A full error analysis has produced standard deviations of both these a_i and further energy coefficients Y_lj. Comparison with experimental data shows good agreement; trends in the hydrogen halide series are discussed.     

The methyl group as phosphate protecting group in nucleotide syntheses

A novel method is described for the removal of a methyl protecting group from phosphotriesters in oligonucleotides.