what is ground state and excited state in chemistry
Excited state The excitation of a system (an atom or molecule) from low-energy excited state to a high-energy excited state with the absorption of a photon is called excited state absorption (ESA). Excited state absorption is possible only when an electron has been already excited from the ground state to a lower excited state. The excited state absorption is usually an undesired effect, but it can be useful in upconversion pumping.[7] The excited state absorption measurements are done using pump-probe techniques. However, it is not easy to measure them compared to ground-state absorption and in some cases complete bleaching of the ground state is required to measure excited state absorption.[8]
Earth Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 7000270000000000000♠2.7 Gya, forming the primarily nitrogen–oxygen atmosphere of today.[71] This change enabled the proliferation of aerobic organisms and, indirectly, the formation of the ozone layer due to the subsequent conversion of atmospheric O2 into O3. The ozone layer blocks ultraviolet solar radiation, permitting life on land.[145] Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature.[146] This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Water vapor, carbon dioxide, methane, nitrous oxide, and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C, in contrast to the current +15 °C,[147] and life on Earth probably would not exist in its current form.[148] In May 2017, glints of light, seen as twinkling from an orbiting satellite a million miles away, were found to be reflected light from ice crystals in the atmosphere.[149][150]
Alonso Álvarez de Pineda
Van der Waals equation is the volume of the container occupied by each particle (not the velocity of a particle), and k is the Boltzmann constant. It introduces two new parameters: a', a measure of the average attraction between particles, and b', the volume excluded from v by one particle.