What part of speech occurs when an adverb is places between the word to and verb stem?

This is a bit of a tricky question! The placement of an adverb between "to" and a verb stem is not a specific grammatical term or "part of speech."

Here's why:

* Adverbs modify verbs, adjectives, or other adverbs. They tell us how, when, where, or to what extent something happens.

* "To" is a preposition when followed by a noun or pronoun (e.g., "to the store"), but it's part of the infinitive form of a verb when followed by the verb stem (e.g., "to run").

The placement of the adverb between "to" and the verb stem is just a grammatical structure, not a distinct part of speech.

Example:

* Incorrect: "I want to quickly run." (This sounds awkward)

* Correct: "I want to run quickly."

In general, adverbs can often be placed in different positions within a sentence. The specific placement can affect emphasis or rhythm.