string[] DateTimeList = { 
                            "yyyy/M/d tt hh:mm:ss", 
                            "yyyy/MM/dd tt hh:mm:ss", 
                            "yyyy/MM/dd HH:mm:ss", 
                            "yyyy/M/d HH:mm:ss", 
                            "yyyy/M/d", 
                            "yyyy/MM/dd" 
                        }; 
 
DateTime dt = DateTime.ParseExact(" 2014/  8/16   PM 03: 20:50  ", 
                                  DateTimeList, 
                                  CultureInfo.InvariantCulture, 
                                  DateTimeStyles.AllowWhiteSpaces
                                  );