Execute workflow using javascript in CRM 2011

function RunWorkflow() {
    var _return = window.confirm('Are you want to execute workflow.');
    if (_return) {
        var url = Xrm.Page.context.getServerUrl();
        var entityId = Xrm.Page.data.entity.getId();
        var workflowId = '437DDF9B-EE32-4E88-91CF-544B49179F58';
        var OrgServicePath = "/XRMServices/2011/Organization.svc/";
        url = url + OrgServicePath;
  var xml = "" +
    "<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
    "<soap:Envelope xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\">" +
    Xrm.Page.context.getAuthenticationHeader() +
    "<soap:Body>" +
    "<Execute xmlns=\"http://schemas.microsoft.com/crm/2007/WebServices\">" +
    "<Request xsi:type=\"ExecuteWorkflowRequest\">" +
    "<EntityId>" + entityId + "</EntityId>" +
    "<WorkflowId>" + workflowId+ "</WorkflowId>" +
    "</Request>" +
    "</Execute>" +
    "</soap:Body>" +
    "</soap:Envelope>";

  var xmlHttpRequest = new ActiveXObject("Msxml2.XMLHTTP");
  xmlHttpRequest.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);
  xmlHttpRequest.setRequestHeader("SOAPAction", "http://schemas.microsoft.com/crm/2007/WebServices/Execute");
  xmlHttpRequest.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
  xmlHttpRequest.setRequestHeader("Content-Length", xml.length);
  xmlHttpRequest.send(xml);
 }
}