Yes, if you are legally separated.
Tax law considers you
"unmarried" if you got a decree of separation maintenance prior to
December 31, you can file with "single" or "head of
household" status.
"Head of household" requires you to have a dependent
and pay at least half of the expenses needed to maintain a home. If your
dependent is a child who lives with you more than with your spouse, the IRS
considers you to be the custodial parent. Your deductions and credits as
custodial parent depend on whether your spouse has agreed to waive his ability
to claim the child as an exemption under Box 6a on the 1040 form -- only one of
you can claim the child as an exemption. When you can claim the dependency
exemption, you can claim child-related credits.