You can initialise a Date object and call getTime() to get it in unix form. It comes out in milliseconds so you’ll need to divide by 1000 to get it in seconds.
(new Date("2013/09/05 15:34:00").getTime()/1000)
It may have decimal bits so wrapping it in Math.round would clean that.
Math.round(new Date("2013/09/05 15:34:00").getTime()/1000)