**Tax Year 2018 or earlier** Can I deduct as alimony my monthly pension payments that i split with my ex wife.

[MargaretL]

Most likely you cannot.  An allocation of your retirement plan (called QDRO) is considered a property settlement and most often it is not alimony. In order for the QDRO payments to be deductible as alimony, it must be specifically classified as such in your divorce decree  Also, the payment must be in cash. 

IRS Pub 504 (page 13-16 discusses the details).