posted on 2024-02-14, 21:05authored byDairen
R. Jean, Samuel A. Wood, Brian J. Esselman, R. Claude Woods, Robert J. McMahon
The
gas-phase rotational spectrum of 1-cyano-2-methylenecyclopropane
(C1, C5H5N), an
isomer of pyridine, is presented for the first time, covering the
range from 235 to 500 GHz. Over 3600 a-, b-, and c-type transitions for the ground
vibrational state have been assigned, measured, and least-squares
fit to partial-octic A- and S-reduced distorted-rotor Hamiltonians
with low statistical uncertainty (σfit = 42 kHz).
Transitions for the two lowest-energy fundamental states (ν27 and ν26) and the lowest-energy overtone
(2ν27) have been similarly measured, assigned, and
least-squares fit to single-state Hamiltonians. Computed vibration–rotation
interaction constants (B0–Bv) using the B3LYP and MP2
levels of theory are compared with the corresponding experimental
values. Based upon our preliminary analysis, the next few vibrationally
excited states form one or more complex polyads of interacting states via Coriolis and anharmonic coupling. The spectroscopic
constants and transition frequencies presented here form the foundation
for both future laboratory spectroscopy and astronomical searches
for 1-cyano-2-methylenecyclopropane.