Least-squares analysis of overlapped bound-free absorption spectra and predissociation data in diatomics: the C(1Πu) state of I2

Formulation and Implementation of Frequency-Dependent Linear Response Properties with Relativistic Coupled Cluster Theory for GPU-Accelerated Computer Architectures

We present the development and implementation of relativistic coupled cluster linear response theory (CC-LR), which allows the determination of molecular properties arising from time-dependent or time-independent electric, magnetic, or mixed electric-magnetic perturbations (within a common gauge origin for the magnetic properties) as well as taking into account the finite lifetime of excited states in the framework of damped response theory. We showcase our implementation, which is capable to offload the computationally intensive tensor contractions characteristic of coupled cluster theory onto graphical processing units, in the calculation of (a) frequency-(in)dependent dipole-dipole polarizabilities of IIB atoms and selected diatomic molecules, with a particular emphasis on the calculation of valence absorption cross sections for the I2 molecule; (b) indirect spin-spin coupling constants for benchmark systems such as the hydrogen halides (HX, X = F-I) as well the H2Se-H2O dimer as a prototypical system containing hydrogen bonds; and (c) optical rotations at the sodium D line for hydrogen peroxide analogues (H2Y2, Y = O, S, Se, Te). Thanks to this implementation, we are able to show the similarities in performance, but often the significant discrepancies, between CC-LR and approximate methods such as density functional theory. Comparing standard CC response theory with the flavor based upon the equation of motion formalism, we find that for valence properties such as polarizabilities, the two frameworks yield very similar results across the periodic table as found elsewhere in the literature; for properties that probe the core region, such as spin-spin couplings, on the other hand, we show a progressive differentiation between the two as relativistic effects become more important. Our results also suggest that as one goes down the periodic table, it may become increasingly difficult to measure pure optical rotation at the sodium D line due to the appearance of absorbing states.

Evolution of a Molecular Shape Resonance along a Stretching Chemical Bond

We report experiments on laser-assisted electron recollisions that result from strong-field ionization of photoexcited I_{2} molecules in the regime of low-energy electron scattering (<25  eV impact energy). By comparing differential scattering cross sections extracted from the angle-resolved photoelectron spectra to differential scattering cross sections from quantum-scattering calculations, we demonstrate that the electron-scattering dynamics is dominated by a shape resonance. When the molecular bond stretches during the evolution of a vibrational wave packet this shape resonance shifts to lower energies, both in experiment and theory. We explain this behavior by the nature of the resonance wave function, which closely resembles an antibonding molecular orbital of I_{2}.

Optimal iodine absorption line applied for spaceborne high spectral resolution lidar

Spaceborne high spectral resolution lidar (HSRL) provides a wide range of observations, e.g., measurements of aerosol backscattering and extinction coefficients and aerosol depolarization ratio with high accuracy, which are of great significance to the study of air pollution monitoring and climate change. With different cells and finger temperatures, the transmittance of the different absorption lines of the iodine vapor filter at 532 nm wavelength was measured. The 1064 nm fundamental frequency pulse energy and the 532 nm frequency-doubled pulse energy output of different seeder laser wavelengths were measured. Based on the relationship among the laser output power, the absorption line shape of the iodine vapor filter, and the atmospheric model, the echo power was calculated and compared. The 1110 iodine absorption line was selected as the optimized filter for the HSRL, which could increase in 22% and 14% efficiency compared with the traditional 1109 line, and a new proposed 1105 line at the 532 nm HSRL channel at 5 km altitude with an enhanced aerosol model, respectively.

Design of iodine absorption cell for high-spectral-resolution lidar

Iodine absorption cells are extensively employed by high-spectral-resolution Lidars (HSRLs) for aerosol optical properties and atmosphere state parameters profiling. To the best of our knowledge, the optimal design of the parameters of iodine cells has not been talked about systematically. In this paper, a heuristic method based on multi-objective concept is proposed for the design of iodine cells employed in HSRLs for aerosol profiling, and the method can be also applied to different types of HSRLs. The bi-objective model is established based on the retrieval error analysis of HSRL and then the Pareto optimal solutions are obtained through the Non-dominated Sorting Genetic Algorithm II (NSGA-II). The performance of different absorption lines are compared according to the Pareto solution sets, and the stability of transmittance characteristics of different absorption lines are discussed through sensitivity analysis. The results are expected to provide guidance for the design of HSRLs based on iodine absorption filters.

High steady-state column density of I((2)P3/2) atoms from I2 photodissociation at 532 nm: Towards parity non-conservation measurements

Steady-state column densities of 10¹⁷ cm⁻² of I(²P_3/2) atoms are produced from photodissociation of I₂ vapour at 290.5 K using 5 W of 532 nm laser light. Recombination of the I(²P_3/2) atoms at the cell walls is minimized by coating the cell surface with a hydrophobic silane (dimethyldichlorosilane/DMDCS). Operation at room temperature, and at an I₂ vapour pressure of ~0.2 mbar, without using a buffer gas, allows relatively low Lorentz and Doppler widths of ~2π × 1.5 (FWHM) and ~2π × 150 (HW at 1/e²) Mrad/s, respectively, at the M1 transition of atomic iodine at 1315 nm. These high column densities and low linewidths are favorable for parity nonconservation optical rotation measurements near this M1 transition. Furthermore, as the cell is completely sealed, this method of production of high-density ¹²⁷I(²P_3/2) atoms is also compatible with using iodine radioisotopes, such as for the production of high-density ¹²⁹I(²P_3/2).

Wavelength anomalies in ultraviolet-visible spectrophotometry

Spectral scans of atomic line emission sources with a Shimadzu UV2101PC spectrophotometer show that the nominal wavelength depends upon the instrumental slit width, the wavelength sampling interval, and for some slit widths, also on the specified spectral range. The range dependence is manifested as a smoothing that occurs when the range includes >65 sampled wavelengths, and it affects both the wavelength and the line shape. For spectra not subject to this smoothing, the wavelength error looks like a one-sample misassociation of the wavelength and photometric readings. However, the instrument does reliably move to a specified wavelength, independent of the scan parameter settings. These behaviors do not seem to be documented anywhere but have been present in the software for operating this instrument for about two decades.

Long-Lived Electronic Coherence of Iodine in the Condensed Phase: Sharp Zero-Phonon Lines in the B↔X Absorption and Emission of I2 in Solid Xe

Our study of B←X absorption of molecular iodine (I2) isolated in a low-temperature crystalline xenon has revealed an exceptionally long-lived electronic coherence in condensed phase conditions. The visible absorption spectrum shows prominent vibronic structure in the form of zero-phonon lines (ZPLs) and phonon side bands (PSBs). The resolved spectrum implies weak interaction of the chromophore to the lattice degrees of freedom. The coherence extends past the vibrational period of the excited state molecule, unlike that observed in any condensed phase environment for I2 so far. The ZP transitions from the relaxing B-state populations were resolved in the hot luminescence when the 532 nm laser was used for excitation.

Analysis of the visible absorption spectrum of I2 in inert solvents using a physical model

Absorption spectra of I(2) dissolved in n-heptane and CCl(4) are analyzed with a quantum gas-phase model, in which spectra at four temperatures between 15° and 50 °C are least-squares fitted by bound-free spectral simulations to obtain estimates of the excited-state potential energy curves and transition moment functions for the three component bands--A ← X, B ← X, and C ← X. Compared with a phenomenological band-fitting model used previously on these spectra, the physical model (1) is better statistically, and (2) yields component bands with less variability. The results support the earlier tentative conclusion that most of the ~20% gain in intensity in solution is attributable to the C ← X transition. The T-dependent changes in the spectrum are accounted for by potential energy shifts that are linear in T and negative (giving red shifts in the spectra) and about twice as large for CCl(4) as for heptane. The derived upper potentials resemble those in the gas phase, with one major exception: In the statistically best convergence mode, the A potential is much lower and steeper, with a strongly varying transition moment function. This observation leads to the realization that two markedly different potential curves can give nearly identical absorption spectra.