Internal conversion is a transition from a higher to a lower electronic state in a molecule or atom. It is sometimes called "radiationless de-excitation", because no photons are emitted. It differs from intersystem crossing in that, while both are radiationless methods of de-excitation, the molecular spin state for internal conversion remains the same, whereas it changes for intersystem crossing. The energy of the electronically excited state is given off to vibrational modes of the molecule. The excitation energy is transformed into heat. == Examples == A classic example of this process is the...

Spectroscopy is the study of the interaction between matter and electromagnetic radiation. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, by a prism. Later the concept was expanded greatly to include any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data are often represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency. == Introduction == Spectroscopy and spectrography are terms used to refer to the measurement of radiat...

Shcha (Щ щ; italics: Щ щ) is a letter of the Cyrillic script. In Russian, it represents the voiceless alveolo-palatal fricative /ɕ(ː)/, like the pronunciation of ⟨sh⟩ in sheep (but longer). In Ukrainian and Rusyn, it represents the consonant cluster /ʃt͡ʃ/. In Bulgarian, it represents the consonant cluster /ʃt/. In Kurdish, it represents the consonant /d͡ʒ/. Other non-Slavic languages written in Cyrillic use this letter to spell the few loanwords that use it or foreign names; it is usually pronounced /ʃ/ and is often omitted when teaching those languages. In English, Shcha is romanized as ⟨shch...