Get thumbnail url outside loop

I’m trying to list some articles with thumbnails as background images outside the loop but nothing seems to be working. I’ve tried using simplexml to get the src (which works) but it breaks the layout after

<?php query_posts('orderby=name&order=asc&cat=9&showposts=4'); ?>
<?php while (have_posts()) : the_post();?>
	<?php $dom = simplexml_load_string(get_the_post_thumbnail()); $thumb = $dom->attributes()->src; ?>
	<li style="background: url('<?php echo $thumb; ?>')" ><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></li>
<?php endwhile;?>

Any other way to do it?