> 4.2nm or 4.2um ? CO2 is absorbing in the near IR or in the far UV ? What's 3 orders of magnitude between friends ? :-) As you imply, its 4.2 um - deepish infrared. Russell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist