Spectroscopy of vibrationally hot molecules: Hydrogen cyanide and acetylene

Thesis/Dissertation · Tue Dec 31 23:00:00 EST 1991

OSTI ID:7006229

Jonas, D M

An efficient formula for calculating nuclear spin statistical weights is presented. New experimental methods to distinguish electric and magnetic multipole transitions are proposed and used to prove that the formaldehyde A - X 0-0 transition is a magnetic dipole transition. HIgh resolution vacuum ultraviolet studies of the A [yields] X fluorescence excitation spectrum of hydrogen cyanide (HCN) have: (i) determined that only the (0,1,0) vibrational level of the HCN A-state has a sufficiently long fluorescence lifetime to be suitable for Stimulated Emission Pumping (SEP) studies; and (ii) measured the electric dipole moment of the A-state. Several transitions in the hydrogen cyanide A [yields] X SEP spectrum are shown to be due to the axis-switching mechanism. From a Franck-Condon plot of the intensities and a comparison between sums of predicted rotational constants and sums of observed rotational constants, all of the remaining transitions in the SEP spectrum can be securly assigned. Two weak resonances; a 2:3 CH:CN stretch Fermi resonance and a 6:2 bend:CN stretch resonance appear in the SEP spectrum. Excitation of the CH stretching vibration is predicted and shown to be entirely absent, apart from resonances, in the HCN SEP spectrum. A [yields] X SEP spectra of acetylene (HCCH) near E[sub VIB] = 7,000 cm[sup [minus]1] display a wealth of strong and fully assignable anharmonic resonances and forbidden rotational transitions. It is proved that Darling-Dennison resonance between the cis and trans bending vibrations is the crucial first step in a series of anharmonic resonances which can transfer nearly all the vibrational energy out of the initial CC stretch/trans-bend excitation at high vibrational energy. Secondary steps in the vibrational energy flow are vibrational-l-resonance and the 2345' Fermi resonance. For short times, the vibrational energy redistribution obeys very restrictive rules.

• Research Organization: Massachusetts Inst. of Tech., Cambridge, MA (United States)
• OSTI ID: 7006229
• Country of Publication: United States
• Language: English

Related Subjects

663220* -- Electromagnetic Transitions-- (1992-)
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ACETYLENE
ALKYNES
CYANIDES
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
HYDROCARBONS
HYDROCYANIC ACID
HYDROGEN COMPOUNDS
INORGANIC ACIDS
M1-TRANSITIONS
MULTIPOLE TRANSITIONS
ORGANIC COMPOUNDS
VIBRATIONAL STATES