Spectra Of I2 Research Articles

Coincidence ion pair production (cipp) spectroscopy of diiodine.

Coincidence ion pair production (I+ + I-) (cipp) spectra of I2 were recorded in a double imaging coincidence experiment in the one-photon excitation region of 71 600-74 000 cm-1. The I+ + I- coincidence signal shows vibrational band head structure corresponding to iodine molecule Rydberg states crossing over to ion-pair (I+I-) potential curves above the dissociation limit. The band origin (ν0), vibrational wavenumber (ωe) and anharmonicity constants (ωexe) were determined for the identified Rydberg states. The analysis revealed a number of previously unidentified states and a reassignment of others following a discrepancy in previous assignments. Since the ion pair production threshold is well established, the electric field-dependent spectral intensities were used to derive the cutoff energy in the transitions to the rotational levels of the 7pσ(1/2) (v' = 3) state.

Shallow Iodine Defects Accelerate the Degradation of α-Phase Formamidinium Perovskite

Summary Shallow defects are mostly benign in covalent semiconductors, such as silicon, given that they do not constitute non-radiative recombination sites. In contrast, the existence of shallow defects in ionic perovskite crystals might have significant repercussions on the long-term stability of perovskite solar cells (PSCs) because of the metastability of the ubiquitous formamidinium lead triiodide (FAPbI3) perovskite and the migration of charged point defects. Here, we show that shallow iodine interstitial defects ( I i ) can be generated unintentionally during commonly used post-fabrication treatments, which can lower the cubic-to-hexagonal transformation barrier of FAPbI3-based perovskites to accelerate its phase degradation. We demonstrate that concurrently avoiding the generation of I i and the more effective passivation of iodine vacancies ( V I ) can improve the thermodynamic stability of the films and operational stability of the PSCs. Our most stable PSC retained 92.1 % of its initial performance after nearly 1,000 h of continuous illumination operational stability testing.

Time-resolved spectra of I2 in a krypton crystal by G-MCTDH simulations: nonadiabatic dynamics, dissipation and environment driven decoherence

The multi-state photodynamics following the B 3Πu(0+) ← X 1Σ+g excitation of molecular iodine in a krypton crystal are studied quantum mechanically using the Gaussian variant of the multiconfigurational time-dependent Hartree method (G-MCTDH). Calculations are performed using a 9-state 18-dimensional Hamiltonian parametrized via diatomics-in-molecules calculations. The simulations reproduce the low predissociation yield deduced by time resolved spectroscopic experiments, and allow the elucidation of the diabatic population dynamics in the dense manifold of covalent electronic states of the embedded I2. The wave packet dynamics are used to calculate pump-probe spectra involving excited state absorption which terminates in the ion pair manifold. The simulated signals are in excellent agreement with the experimental ones, and are interpreted by reducing the full-dimensional wavefunction to the density matrix of the I2 subsystem. It is proved formally that the pump-probe traces can be obtained as convolution between the Wigner function of the chromophore and a time- and frequency-gate function also represented in the phase space. The analysis of the spectra with probe frequency in resonance with the β ← A 3Πu transition reveals that the mechanism of predissociation out of the B state is pump photon energy-dependent. The quantum nature of the nonradiative transitions is imprinted in the strongly non-classical features of the Wigner function on the A state surface, which is detected in the pump-probe process.

The spin-forbidden a 4Σ--X 2Π1/2 transition of GeH detected in absorption using intracavity laser spectroscopy.

The a 4Σ--X 2Π1/2 transition of GeH has been recorded in absorption for the first time using Intracavity Laser Spectroscopy (ILS). The GeH molecules were produced in a 0.40-0.60 A DC plasma discharge inside an aluminum hollow cathode, using 500 mTorr of Ar, 100 mTorr of H2, and 200 mTorr of GeH4. This cathode is located within the resonator cavity of a Coherent Verdi™ V-10 pumped dye laser. Effective path lengths for this series of measurements using the ILS method ranged from 2 to 7 km. Spectra were calibrated using the absorption spectrum of I2 collected from an extracavity cell, the I2 transmission spectrum from Salami and Ross, J. Mol. Spectrosc. 223(1), 157 (2005) and PGOPHER's [C. M. Western, J. Quant. Spectrosc. Radiat. Transfer 186, 221-242 (2016)] calibration feature. Differences in peak positions between calibrated experimental spectra and the reference data were on average less than ±0.002 cm-1. All eight branches expected to have appreciable intensity for the transition have been identified, and isotopologue splitting was observed in features of 5 of the 8 identified rotational branches. Molecular constants have been obtained for the a 4Σ- states of 70GeH (20.84% abundant), 72GeH (27.54% abundant), and 74GeH (36.28% abundant). The transitions were fit using PGOPHER, holding the ground state constants fixed to the values reported by Towle and Brown [Mol. Phys. 78(2), 249 (1993)]. The constants for the a 4Σ- state of 74GeH determined by the fit are T0 = 16 751.5524(13) cm-1, B0 = 6.764 912(33) cm-1, D0 = 0.459 60(17) × 10-3 cm-1, λSS = 9.7453(12) cm-1, λD = 0.468(14) × 10-3 cm-1, γ = 0.077 878(84), and γS = -0.361(77) × 10-3 cm-1.

Spectra of I2+ for possible measurement of α and μ constant

分子离子I2+的禁戒跃迁光谱有可能用于测量α和μ常数的变化，并且具有增强的灵敏度.通过分析I2+在11860–13100 cm-1范围内的转动光谱，拟合了A2Π3/2-X2Π3/2系统31个振转带的5759根吸收谱线，得到5个属于X2Π3/2态和9个属于A2Π3/2态的振动能级准确的转动光谱常数.在量子噪声极限和1 Hz跃迁线宽的条件下，计算得到X2Π3/2和X2Π1/2之间的禁戒跃迁对α和μ常数变化测量的灵敏度为δα/α ≈ 2.37×10-19a-1和δμ/μ ≈ 1.18×10-18a-1.

Heavy Rydberg behaviour in high vibrational levels of some ion-pair states of the halogens and inter-halogens.

We report the identification of heavy Rydberg resonances in the ion-pair spectra of I2, Cl2, ICl, and IBr. Extensive vibrational progressions are analysed in terms of the energy dependence of the quantum defect δ(Eb) rather than as Dunham expansions. This is shown to define the heavy Rydberg region, providing a more revealing fit to the data with fewer coefficients and leads just as easily to numbering data sets separated by gaps in the observed vibrational progressions. Interaction of heavy Rydberg states with electronic Rydberg states at avoided crossings on the inner wall of the ion-pair potential is shown to produce distinctive changes in the energy dependence of δ(Eb), with weak and strong interactions readily distinguished. Heavy Rydberg behaviour is found to extend well below near-dissociation states, down to vibrational levels ∼18,000-20,000 cm(-1) below dissociation. The rapid semi-classical calculation of δ(Eb) for heavy Rydberg states is emphasised and shows their absolute magnitude to be essentially the volume of phase space excluded from the vibrational motion by avoiding core-core penetration of the ions.

Folding and Unfolding Pathways of the Human Telomeric G-Quadruplex

Sequence analogs of human telomeric DNA such as d[AGGG(TTAGGG)3] (Tel22) fold into monomeric quadruplex structures in the presence of a suitable cation. To investigate the pathway for unimolecular quadruplex formation, we monitored the kinetics of K+-induced folding of Tel22 by circular dichroism (CD), intrinsic 2-aminopurine fluorescence, and fluorescence resonance energy transfer (FRET). The results are consistent with a four-step pathway U ↔ I1 ↔ I2 ↔ I3 ↔ F where U and F represent unfolded and folded conformational ensembles and I1, I2, and I3 are intermediates. Previous kinetic studies have shown that I1 is formed in a rapid pre-equilibrium and may consist of an ensemble of “prefolded” hairpin structures brought about by cation-induced electrostatic collapse of the DNA. The current study shows that I1 converts to I2 with a relaxation time τ1=0.1s at 25°C in 25mM KCl. The CD spectrum of I2 is characteristic of an antiparallel quadruplex that could form as a result of intramolecular fold-over of the I1 hairpins. I3 is relatively slowly formed (τ2≈3700s) and has CD and FRET properties consistent with those expected of a triplex structure as previously observed in equilibrium melting studies. I3 converts to F with τ3≈750s. Identical pathways with different kinetic constants involving a rapidly formed antiparallel intermediate were observed with oligonucleotides forming mixed parallel/antiparallel hybrid-1 and hybrid-2 topologies {e.g. d[TTGGG(TTAGGG)3A] and d[TAGGG(TTAGGG)3TT]}. Aspects of the kinetics of unfolding were also monitored by the spectroscopic methods listed above and by time-resolved fluorescence lifetime measurements using a complementary strand trap assay. These experiments reveal a slow, rate-limiting step along the unfolding pathway.

Dynamics Behind the Long-Lived Coherences of I2 in Solid Xe

The absorption spectrum of I2 in solid Xe shows resolved zero-phonon lines and phonon side bands near the origin of the B←X transition (550-625 nm). The long-lived |B⟩⟨X| coherence in this energy range (T2 = 600 fs on average) emerges as vibrationally unrelaxed fluorescence in resonance Raman (RR) spectra. Upon excitation in the structureless continuum at 532 nm, the oscillatory RR progression exhibits electronic dephasing time of T2 = 150 fs. Two RR progressions with markedly different vibrational coherence on the X-state are observed. The main progression of sharp overtones (T2 > 21 ps) is assigned to molecules trapped in double-substitution sites. The minor progression, which shows dephasing times T2 = 6-0.6 ps for v = 1-8, is assigned to molecules in triple-substitution sites. The line progressions allow a detailed characterization of the solvated B- and X-state potentials. Time-resolved coherent anti-Stokes Raman scattering is used to probe selected vibrational coherences on the X-state. Assignments are obtained through molecular dynamics simulations, which reproduce the relative dephasing rates between the two sites, clarify the role of rotation-translation dynamics, and enable quantum dynamics simulations of the spectra by the potentials of mean force that accurately describe the molecule-surrounding interactions.

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.

Structure, energy, and IR spectra of I2∙−.nH2O clusters (n=1–8): A theoretical study

The authors report theoretical results on structure, bonding, energy, and infrared spectra of iodine dimer radical anion hydrated clusters, I(2) (-).nH(2)O (n=1-8), based on a systematic study following density functional theory. Several initial guess structures are considered for each size cluster to locate minimum energy conformers with a Gaussian 6-311++G(d,p) split valence basis function (triple split valence 6-311 basis set is applied for iodine). It is observed that three different types of hydrogen bonded structures, namely, symmetrical double hydrogen bonding, single hydrogen bonding, and interwater hydrogen bonding structures, are possible in these hydrated clusters. But conformers having interwater hydrogen bonding arrangements are more stable compared to those of double or single hydrogen bonded structures. It is also noticed that up to four solvent H(2)O units can reside around the solute in interwater hydrogen bonding network. At the maximum six H(2)O units are independently linked to the dimer anion having four double hydrogen bonding and two single hydrogen bonding, suggesting the hydration number of I(2) (-) to be 6. However, conformers having H(2)O units independently linked to the iodine dimer anion are not the most stable structures. In all these hydrated clusters, the odd electron is found to be localized over two I atoms and the two atoms are bound by a three-electron hemi bond. The solvation, interaction, and vertical detachment energies are calculated for all I(2) (-).nH(2)O clusters. Energy of interaction and vertical detachment energy profiles show stepwise saturation, indicating geometrical shell closing in the hydrated clusters, but solvation energy profile fails to show such behavior. A linear correlation is observed between the calculated energy of interaction and vertical detachment energy. It is observed that formation of I(2) (-)-water cluster induces significant shifts from the normal O-H stretching modes of isolated H(2)O. However, bending mode of H(2)O remains insensitive to the successive addition of solvent H(2)O units. Weighted average energy profiles and IR spectra are reported for all the hydrated clusters based on the statistical population of individual conformers at room temperature.

Photoelectron imaging of I2− at 5.826eV

We report the anion photoelectron spectrum of I2- taken at 5.826 eV detachment energy using velocity mapped imaging. The photoelectron spectrum exhibits bands resulting from transitions to the bound regions of the X 1Sigmag+(0g+), A' 3Piu(2u), A 3Piu(1u), and B 3Piu(0u+) electronic states as well as bands resulting from transitions to the repulsive regions of several I2 electronic states: the B' 3Piu(0u-), B" 1Piu(1u), 3Pig(2g), a 3Pig(1g), 3Pig(0g-), and C 3Sigmau+(1u) states. We simulate the photoelectron spectrum using literature parameters for the I2- and I2 ground and excited states. The photoelectron spectrum includes bands resulting from transitions to several high-lying excited states of I2 that have not been seen experimentally: 3Pig(0g-), 1Pig3(1g), 1 3Sigmag-3(0g+), and the 1Sigmag-3(0u-) states of I2. Finally, the photoelectron spectrum at 5.826 eV allows for the correction of a previous misassignment for the vertical detachment energy of the I2 B 3Piu(0u+) state.

Experimental and theoretical investigations of the He⋯I2 rovibronic spectra in the I2 B–X, 20–0 region

The laser-induced fluorescence and action spectra of I2 in a helium supersonic expansion have been recorded in the I2 B-X, 20-0 region. Two features are identified within the spectra. The lower-energy feature arises from transitions between states that are localized in a T-shaped conformation on both the X- and B-state potentials. The higher-energy feature reflects transitions from states that are localized in a linear conformation on the X state to states that have energies that are larger than the barrier for free rotation of the rare gas atom about the I2 molecule on the B-state potential. Ground-state binding energies of 16.6(6) and 16.3(6) cm-1 were determined for the T-shaped and linear conformers, respectively. These spectra are compared to those calculated using the experimentally determined rotational temperatures. Based on the agreement between the experimental and calculated spectra, the binding energies of the J'=0 states with 0 and 2-6 quanta of excitation in the He...I2 bending mode on the B state were determined. Several models for the B-state potential were used to investigate the origins of the shape of the contour of the higher-energy feature in the spectra for He...I2 and He...Br2. The shape of the contours was found to be relatively insensitive to the choice of potential. This leads us to believe that the spectra of these systems are relatively insensitive to the parameters of the B-state potential energy surface and are more sensitive to properties of the halogen molecule.

Effects of column density on I<sub>2</sub> spectroscopy and a determination of I<sub>2</sub> absorption cross section at 500 nm

Abstract. The use of ro-vibronic spectra of I2 in the region of 543 nm to 578 nm as reference spectra for atmospheric Differential Optical Absorption Spectroscopy is studied. It is shown that the retrieval of atmospheric column densities with Differential Optical Absorption Spectroscopy set-ups at FWHM at and above 1 nm depends critically on the column density, under which the used reference spectrum was recorded. Systematic overestimation of the comparatively low atmospheric column density of I2 of the order of 13% is possible. Under low pressure conditions relevant in laboratory studies, the systematic deviations may grow up to 45%. To avoid such effects with respect to field measurements, new reference spectra of I2 were determined under column density of the order of 1016 cm-2 close to that expected for an atmospheric measurement. Two typical configurations of Differential Optical Absorption Spectroscopy, which use grating spectrometers, were chosen for the spectroscopic set-up. One spectrum was recorded at similar resolution (0.25 nm FWHM) but finer binning (0.035 nm/pixel) than previously published data. For the other (0.59 nm FWHM, 0.154 nm/pixel) no previously published spectra exist. Wavelength calibration is accurate to ±0.04 nm and ±0.11 nm respectively. The absorption cross section for the recordings was determined under low column density with an accuracy of ±4% and ±3% respectively. The absolute absorption cross section of I2 at 500 nm (wavelength: in standard air) in the continuum absorption region was determined using a method independent of iodine vapour pressure. Obtained was σI2 (500 nm)=(2.186±0.021·10-18 cm2 in very good agreement with previously published results, but at 50% smaller uncertainty. From this and previously published results a weighted average of σI2(500 nm)=(2.191±0.02)·10-18 cm2 is determined.

Need a single-mode red laser, cheap? Check your pockets!

An inexpensive (<$5) key-chain model of red laser pointer (RLP) operates with typically 98% of its total emission in a single longitudinal cavity mode. The laser self-tunes with time, interpreted as due to thermal effects. The laser can also be tuned by varying its operating current and voltage. These properties permit one to quickly and easily record absorption spectral segments spanning ranges of 1–6cm−1, with high quantitative reliability, resolution, and accuracy. As examples, spectra of I2 are recorded in the 650nm region as a function of pressure for several RLP wavelengths and are used to estimate the strength of the underlying continuum (due to A←X absorption) with relative standard error less than 1%. Similarly, measurements of the integrated line absorption on selected lines in the B←X transition yield estimates of the electronic transition strength with unprecedented precision.

Ultrafast nonadiabatic dynamics: quasiclassical calculation of the transient photoelectron spectrum of I2(-).(CO2)8.

In this paper we investigate the transient photoelectron spectrum of I2(-) in CO2 clusters recently measured by Neumark and co-workers. This work reveals a rich excited state dynamics with various competing electronic output channels. We find good agreement with experiments and we are able to relate the transient signal to different dynamical events that occur during the evolution of the cluster and its fragmentation products.

Anion photoelectron spectroscopy of I2−(CO2)n(n=1–8) clusters

We report the anion photoelectron spectra of I2−(CO2)n clusters (n=1–8) measured at a photon energy of 4.661 eV. Assignment of the spectra is aided by electronic structure calculations on I2−(CO2). The experiment yields size-dependent vertical and adiabatic detachment energies for the formation of the ground state and low-lying valence-excited states of the neutral cluster. Vertical detachment energies are successively blueshifted with increasing cluster size, indicating a stronger stabilization of the anionic cluster relative to the neutral counterpart. In addition, a short progression in the CO2 bending mode is observed in the n=1 and 2 clusters, indicating that the CO2 solvent species are slightly bent (∼2.5°) in the anion clusters. The trends in the total and stepwise solvation energies are discussed in terms of cluster geometries solute–solvent interactions.

A re-analysis of the vacuum ultraviolet absorption spectrum of I2, Br2, and ICl using ionization energies determined from their ZEKE-PFI photoelectron spectra

The vacuum ultraviolet absorption spectra of I2, Br2 and ICl have been re-analysed using new data from the zero kinetic energy-pulsed field ionization (ZEKE-PFI) photoelectron spectra of all three molecules, and the (2 + 1) resonance enhanced multiphoton ionization (REMPI) spectrum of ICl. A common pattern of absorption intensities emerges in which all transitions to states which have appreciable singlet character are strong. Thus, in all three molecules, strong transitions are observed to four np and six nf Rydberg series based on the X[2Π3/2]g and X[2Π1/2]g states of the molecular ions, to two ns and six nd states in ICl and to two ns states based on the A[2Π3/2]u and A[2Π1/2]u states of the ion in Br2. The Ω values of some of the Rydberg series have been determined directly from the (2 + 1) REMPI spectrum of ICl.

Component Analysis of the Visible Absorption Spectra of I2 and Br2 in Inert Solvents: A Critique of Band Decomposition by Least-Squares Fitting

The absorption spectra of I2 and Br2 dissolved in n-heptane and CCl4 are recorded with high precision in the visible-near-IR spectral range, at temperatures between 15° and 50 °C. The spectra are decomposed into the three contributing transitions (1Πu ← X, B0+u3Π ← X, and A 1u3Π ← X) through simultaneous least-squares fitting of the T-dependent data. The main results of the analysis are as follows. (1) In I2 the weakest A ← X band is virtually identical in shape and intensity in these solvents and in the gas phase, but with small blue shifts in solution. (2) The ∼20% increased absorption of I2 in solution appears to be largely attributable to a doubling in the intensity of the weaker of the two main transitions, 1Πu ← X, which is red-shifted in solution. (3) All three transitions in I2 shift to the red with increasing T, with the strongest effect observed for 1Πu ← X. These differences are not explained by the refraction-index-based relations commonly used to relate gas- and condensed-phase spectra. In the course of this work the method of decomposition analysis by fitting to assumed band shapes has been tested extensively, with the following observations. (1) The much-used 3-parameter Gaussian and log-normal functions do not have enough flexibility to fit single “pure” bands within the experimental precision obtainable from commercial spectrophotometers. (2) The results of such analyses can vary widely with choice of band function. (3) When comparing two such analyses, lower variance is no guarantee of a “truer” resolution. Concerning the labeling of the halogen electronic states involved in the absorption, it is recommended that for consistency the 1Πu state be designated as the C state in all the halogens.

Theoretical spectroscopy of molecular iodine. 1. Ab initio study on the B0+ u − X0+ g, A1u − X0+ g and B′1u − X0+ g radiative transition intensities

Ab initio quasirelativistic calculations on the B0+ u − X0+ g, A1u (1Πu)-X0+ g transition dipole moment functions for the I2 molecule are reported. The computational approach combines a description of relativistic effects through core pseudopotentials with correlation treatment by many-body multipartitioning perturbation theory. The resulting functions are used to simulate the absorption spectra of I2 and to estimate the radiative decay rates of the B0+ u,v′ states.

On the Role of Statistical Weighting in the Least-Squares Analysis of UV-Visible Spectrophotometric Data

Spectrophotometric data are inherently heteroscedastic, which means that least-squares component analyses of absorbance spectra should properly employ weighted fits. The effects of neglecting weights (the common practice) is examined through Monte Carlo calculations on a three-peak model having two closely overlapping components of comparable strength and a third component that appears as a weak shoulder. The results show statistically significant loss of precision in all parameters; however the magnitude of this loss is ≤30% for realistic conditions. For comparison, experimental spectra of I2 in CCl4 (which was the basis for the Monte Carlo test model) are similarly analyzed. These results suggest that model inadequacy is likely to be a greater practical problem than neglect of weights, because the great precision of spectrophotometric data places extreme demands on the fit model. In the present instance, for example, incorporation of a correction term for the sinusoidal error in the spectrometer wavelength significantly reduces the fit chi-square.