From owner-chemistry@ccl.net Thu Sep 17 20:30:00 2015 From: "Dom Esan desan2^_^uic.edu" To: CCL Subject: CCL: Isotopic Vibrational Frequencies in g09 Message-Id: <-51749-150917202918-1478-0iJJwONwauzqU8L0Cs57tw#server.ccl.net> X-Original-From: "Dom Esan" Date: Thu, 17 Sep 2015 20:29:17 -0400 Sent to CCL by: "Dom Esan" [desan2]![uic.edu] Good day all, I ran some vibrational frequency calculations using different atomic isotopes in g09 but I'm getting some "weird" results. Basically, I used the checkpoint file from a previous frequency calculation of a non-substituted molecule (CH2NH2, say) and then used "readfc and readisotopes" to calculate the frequencies of substituted isotopes of C or N (13C or 15N). The resultant frequencies from the isotopic calculations were *higher* than those of the non-substituted molecule(s). One would expect the frequencies of the heavier isotopes to be *lower*. Does anyone have any suggestions as to what might be wrong? All calculations were done on a metal cluster with the metal atoms frozen. Thank you for your time and anticipated assistance.