Green light, for some reason, penetrates better into lower-lying leaves and allows them to photosynthesize better. It turns out that green light is actually very useful for plants, and although it is the most reflected light it does serve a purpose, with the plant still managing to use most of the green light thrown at it. Scientists can create "action spectrums" that show what wavelengths of light result in the most oxygen produced (to measure the amount of photosynthesis). No pigment really absorbs green light best, which is why its reflected and most plants are green or greenish. If a plant has more carotene, for example, it would better absorb orange light. Different types of pigments absorb different wavelengths of light, and some plants have more of one type than others. Chem.Interesting question! Whether the plant would be able to live or not depends both upon the plant itself and the wavelength of the light. Ara Apkarian, Everyly Fleischer, and Kenneth C. Reference: Spectroscopic Signatures of Halogens in Clathrate Hydrate Cages. These observations are shown to be consistent with a strong interaction between a water molecule and iodine through the loan pair of electrons on water as in the case of bromine in the same media. In contrast, in water and in ice, the valence absorption band of I 2 is dramatically broadened and blue-shifted by 3000 cm -1. We conclude that iodine in sII hydrate resides in a 5 126 4 cavity, in which the ground-state I 2 potential is not significantly perturbed by the hydrate lattice. This is mainly ascribed to the differential solvation of the I 2 electronic states. (In the gas phase or in some inert solvent iodine has a violet color, not rose). UV-visible absorption spectrum of iodine in sII hydrate exhibits a relatively large, 1440 cm -1, blue shift. The process is reversible and the yellow iodine/THF/water solution turns rose again upon clathrate hydrate formation below 4.40 C. The rose-colored clathrate turns yellow as it decomposes. The figure shows the remarkable color change upon melting of the I 2 doped THF clathrate hydrate. The iodine concentration was always less than one percent of the hydrate forming molecule, and more typically 0.1 percent. We chose again to make double sII hydrate using the clathrate forming molecules THF, CH 2Cl 2 and CHCl 3 with iodine as a second guest. Even though iodine does not stabilize the clathrate hydrate lattice by itself, it has the appropriate diameter to fit into the 5 126 4 cages of sII structure. Iodine molecule is another halogen that is widely used as a probe of local environment. The THF or CH 2Cl 2 molecules occupy most of the larger cages, but in this study a small fraction of the large cages is occupied by bromine molecules(Section (B) on the above figure shows THF hydrate doped with bromine. Also, we studied low concentrations of trapped bromine molecules in type II hydrate cages formed with either tetrahydrofuran (THF,C 4H 8O) or methylene chloride (CH 2Cl 2) as the principle hydrate-former guest molecule. To circumvent this issue, we make thin films of polycrystalline bromine clathrate hydrate and study them at temperatures where the halogen vapor pressure is negligible. The halogen clathrate hydrates optical density in a pure crystal is extremely high. In the clathrate hydrates, the oxygen lone-pair orbitals are all involved in the hydrogen-bonded water lattice and are thus unavailable to interact with the halogen guest molecule. The shift and broadening in water and ice is due to the strong interaction of the water lone-pair orbitals with the halogen ó* orbital. For example, the absorption bands shift by about 360 cm -1 for bromine in large 5 126 4 cages of type II clathrate, by about 900 cm -1 for bromine in 5 126 2 cages of pure bromine hydrate, and by more than 1700 cm -1 for bromine in liquid water or amorphous ice. Here we use Uv-visible absorption spectroscopy to track changes in absorption spectra for halogens from the gas phase to clathrate hydrate environment and to liquid water/amorphous ice. Similarly, they are often used to observe how the local environment affects electronic structure, for example, in noble gas matrices, solvents,or microporous SiO 2. They serve as model systems for nonlinear optical studies, energy transfer studies, and cluster studies. UV-VIS ABSORPTION SPECTROSCOPY OF HALOGEN CLATHRATE HYDRATESĭihalogen molecules are often employed as spectroscopic model systems due to their intense optical spectra and relatively easily assignable orbital symmetries.
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