onLoad not firing

I have a modal frame popup, and would like to run some jQuery code after it loads. I can't seem to get the onLoad event to fire. Here's my code:

var modalFrameOptions = {
  url : "http://google.com",
  width : 800,
  height : 600
};
modalFrameOptions.onLoad = function(modalFrame, $iFrameWindow, $iFrameDocument) {
  alert('child onLoad ran');
}
Drupal.modalFrame.open(modalFrameOptions);

The dialog pops up but no alert is displayed.

I have also tried:

var modalFrameOptions = {
  url : "http://google.com",
  width : 800,
  height : 600,
  onLoad : documentLoad()
};
Drupal.modalFrame.open(modalFrameOptions);

function documentLoad(modalFrame, $iFrameWindow, $iFrameDocument) {
  alert('commentFormLoad');
  alert(modalFrame);
  alert($iFrameWindow);
  alert($iFrameDocument);
}

In this case, the alerts display, but all of the argument objects are "undefined".

Is there some other way to manipulate the child modal popup with jQuery?

Thanks for your help!