What is the expiation for an oath of divorce, "By divorce, if I go to that land," and does it have a special ruling if it is the third such oath?

If you intended for the divorce to occur by your going to the mentioned land, then it takes effect. However, if you did not intend divorce but rather an oath, then you must perform an expiation for an oath (kaffarat yamin) according to some meticulous scholars. This involves feeding ten poor persons, or clothing them, or freeing a slave. If you cannot find any of these, then you must fast for three days, as Allah the Almighty says: "So its expiation is the feeding of ten poor persons from the average of that which you feed your [own] families or clothing them or freeing a slave. But whoever finds not [the means to do so] - then a fast of three days. That is the expiation for your oaths when you have sworn. And guard your oaths. Thus does Allah make clear to you His verses that you may be grateful." It is important to note that swearing by anyone other than Allah the Almighty is not permissible.