In Classical Athens, raping a woman was thought to be a less serious crime than moicheia, which is usually translated as 'adultery', but encompassed having sex with any woman under a man's guardianship: his wife, his unmarried daughters, his unmarried sisters if his father had died, in fact, any unmarried female relative who had no closer male relative. There were two reasons for this:
Rape was thought to be generally unpremeditated; seduction was not.
Seduction involved capturing the woman's loyalty, and so was a severer crime against the woman's kyrios (guardian).
The penalty for forcible rape (as described in Lysias 1 and Plutarch's biography of Solon) appears to have been a fine; the penalty for moicheia could, if the kyrios of the seduced woman caught the culprits in the act, be imprisonment until a fine was paid (by the victim, not the state), or death (Lysias' speech Against Erastothenes concerns a man who killed someone called Euphiletos when he caught him having sex with his wife. He is defending himself on a murder charge with the defence that as he caught Euphiletos in the act, he is legally permitted and morally obliged to kill him). It seems that a man who caught his wife committing adultery was legally obliged to divorce her, and she would no longer be permitted to take part in public religious ceremonies (these laws come from Demosthenes Against Neaira).
Charges of sexual assault were apparently prosecuted as general assault charges, or as charges of hubris (a kind of assault which caused shame or dishonour to the victim). Neither of these charges were specifically sexual, and there was no specific crime of sexual assault.
Sources
Susan Guettel Cole, "Greek Sanctions Against Sexual Assault"
K.J. Dover, "Classical Greek Attitudes to Sexual Behaviour"
Sarah B. Pomeroy, Goddesses, Wives, Whores, and Slaves: Women in Classical Antiquity
Lysias 1 (Against Erastothenes)
Demosthenes 59 (Against Neaira)