The molecular structure of HCO+ by the microwave substitution method

Abstract

Precise measurements of the frequencies of the J = 0–1 transition of HCO⁺, H¹³CO⁺, HC¹⁸O⁺, DCO⁺, D¹³CO⁺, and DC¹⁸O⁺ have been used to determine a substitution (r_s) molecular structure for HCO⁺. The bond distances obtained are r_s(CO) = 1.1071(2) Å and r_s(CH) = 1.0930(1) Å. This is the first such microwave r_s structure to be determined for any molecular ion. The determined bond distances and the transition frequencies can be compared to the results of previous high quality ab initio calculations and excellent agreement is found. An initial attempt to characterize the Doppler shifts of the HCO⁺ frequency due to ion drift in a dc discharge and a measurement of the J = 1→2 transition of DCO⁺, and thus its centrifugal distortion constant, are also reported here.