You're asking for a common fact, about a molecule that's been known for at least a century. In a situation like that, you should try Wikipedia first:
http://en.wikipedia.org/wiki/Ozone#Structure I'm sorry that section doesn't have a particular reference cited. But, you should check to references at the bottom of the page. Or maybe the references given in a textbook, if they do that. Or a quick literature search for ozone, pick any recent article, then check it's intro for references, to see if you can get an early discussion on the topic.
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For example, start here:
http://jcp.aip.org/resource/1/jcpsa6/v66/i12/p5278_s1?isAuthorized=no if you can get access to that article, it may start with references to the structure of ozone