What am I doing wrong here?

I am attempting to return a json object and I can't seem to get past the array... I've built hundreds of regular array and returned them as a json object but I am having a hard time wrapping my head around this one.

$rows = array();
$post_array = array();

$i = 0;

$result = mysql_query(" SELECT * FROM forum_posts WHERE permalink = '$permalink' AND LOWER(raw_text) LIKE '%$str%' " );


while($row = mysql_fetch_assoc($result))
    {
        $post_array[$i] = $rows[  "id" => htmlentities($row["id"]),
                                        "post_content" => htmlentities($row["content"]),
                                        "author" => $row["author"],
                                        "last_updated" => $row["last_updated"],
                                        "author_id" => $row["author_id"],
                                        "editing_author" => $row["editing_author"],
                                        "date" => $outputQuoteDate  ];
        $i++;
    }