JSON.stringify problems

In the code below, I am trying to send a JSON encoded javascript object.

However, when the object is json "stringified", it removes the eventcode, price and WaitingList values.
In the JSON result (json_data), all I see is the firstname, lastname, email for each particpant that was added.

How do I prevent this from happening. The eventcode, price and WaitingList values are global for all participants.

    window.particpants = [];
    window.participants['eventcode']   = "GEVENT";
    window.participants['price']       = 99.00;
    window.participants['WaitingList'] = "";

    if(waiting_list_flag) {
      window.participants['WaitingList'] = "YES";
    } else {
      window.participants['WaitingList'] = "NO";
    }

    $('#next_btn').click(function() {
      addParticipant(); // adds the last entered participant info to the participants object
      var url = AJAX_URL_ADD
      json_data = JSON.stringify(window.participants); // json encode the participants

      $.ajax({async: false, 
              type:'POST',
              url: url, 
              data: json_data, 
              dataType: 'json', 
              contentType: "application/json; charset=utf-8", 
              success: function(data){
                if(data.result=='success') {
                  window.location = GOTO_URL;
                } else {
                  //display error
                  $('.error_message').html(data.message);
                } // if(data.result=='success')
              } // success function()
      }); // $.ajax
    }); // $('#next_btn').click

  // also called from another button click to add more participants
  function addParticipant() {
    var participant = {};
    participant.firstname   = $('#FirstName').val();
    participant.lastname    = $('#LastName').val();
    participant.email       = $('#Email').val();
    window.participants.push(participant);
  } // function addParticipant()

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