Yes, you can create a promo code specifically for certain products in magento.
Login in Backend >> Promotions -> Shopping Cart Price Rules >> Press “Add New Rule” button and fill out all info.
Now click on left “condition” Tab and than select “product attribute combination” After that select “SKU” on dropdown
Now fill out all left tab and Save the rule. and check it on frontend for particular product.
NOTE:- if you can’t find SKU on drop down than follow below step to see the SKU on product attribute combination
Go to Catalog >> Attributes >> click Manage Attribute >> search sku on Attribute code and click on it . than find “Use for Promo Rule Conditions” and set this YES
