What is the regex for date and date with time

I have a excel file in that there is a date column, in some of the row I have date with time and some of the row having date without time there is also some other columns after date column to write regex. I have used this : (?(\d+/\d+/\d+)\s(\d+:\d+:\d+)) but this is not able to match date without time.

23/03/2015 16:02:34 employeename1