Simple Q&A D&D 3.5 (by RAW) XX

[mattie_p]

A958 dissent.

A creature can grope about to find an invisible creature. A character can make a touch attack with his hands or a weapon into two adjacent 5-foot squares using a standard action.

So it seems a safe assumption that a generic touch attack as you described takes a standard action and does not provoke attacks of opportunity (as one is not mentioned there).

I'm afraid it is not a safe assumption, the key word "attack" refers to the rules on actions in combat.

"Armed" Unarmed Attacks
Sometimes a character’s or creature’s unarmed attack counts as an armed attack. A monk, a character with the Improved Unarmed Strike feat, a spellcaster delivering a touch attack spell, and a creature with natural physical weapons all count as being armed.

Unless the character is groping with their weapon or has an "armed" unarmed attack in accordance with the list above, waving your hands in the face of an invisible character, hoping to find them, will provoke an attack of opportunity.