chemistry

Internal conversion (chemistry)

Internal conversion (chemistry) is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Internal conversion (chemistry) rather than just read about it. In short: 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.

Key takeaways

Internal conversion (chemistry) belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Internal conversion (chemistry) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Internal conversion (chemistry) from memory before moving on to harder problems.

Reference excerpt

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 Several natural molecules perform a fast internal conversion. This ability to transform the excitation energy of photon into heat can be a crucial property for photoprotection by molecules such as melanin. Fast internal conversion reduces the excited state lifetime, and thereby prevents bimolecular reactions. Bimolecular electron transfer always produces a reactive chemical species, free radicals. Nucleic acids (precisely the single, free nucleotides, not those bound in a DNA/RNA strand) have an extremely short lifetime due to a fast internal conversion. Both melanin and DNA have some of the fastest internal conversion rates. In applications that make use of bimolecular electron transfer the internal conversion is undesirable. For example, it is advantageous to have a long-lived excited state in Grätzel cells (Dye-sensitized solar cells).

See also Fluorescence spectroscopy Förster resonance energy transfer

References

Illustrations

Worked examples

Example 1 — a first encounter with Internal conversion (chemistry)

Start with the simplest possible case. Write down what Internal conversion (chemistry) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Internal conversion (chemistry) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Internal conversion (chemistry) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Internal conversion (chemistry)

In research: Internal conversion (chemistry) appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Internal conversion (chemistry) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Internal conversion (chemistry) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fluorescence, Photochemistry, Spectroscopy, so understanding it makes those chapters shorter.
In everyday life: Look for Internal conversion (chemistry) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Internal conversion (chemistry) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Internal conversion (chemistry) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Internal conversion (chemistry) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Internal conversion (chemistry) in simple terms?

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.

Why does Internal conversion (chemistry) matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Internal conversion (chemistry)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Internal conversion (chemistry).